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Calcium-Mediated Catalytic Hydroamination and

Hydrophosphanylation Reactions

D I S S E R T A T I O N

Zur Erlangung des akademischen Grades doctor rerum naturalium

(Dr. rer. nat.)

vorgelegt dem Rat der Chemisch-Geowissenschaftlichen Fakultät

der Friedrich-Schiller-Universität Jena

von B.Sc. Fadi Younis

geboren am 24.05.1988 in Damaskus (Syrien)

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Gutachter:

1. Prof. Dr. M. Westerhausen 2. Prof. Dr. R. Beckert

Tag der öffentlichen Verteidigung: 14.09.2016

,,Gedruckt bzw. veröffentlicht mit Unterstützung des Deutschen $NDGHPLVFKHQ$XVWDXVFKGLHQVWHVµµ

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ÄMan kann nicht hoffen, die Welt zum Besseren zu wenden, wenn sich der Einzelne nicht zum Besseren wendet. Dazu sollte jeder von uns an seiner eigenen Vervollkommnung arbeiten und sich dessen bewusst werden, dass er die persönliche Verantwortung für alles trägt, was in dieser Welt geschieht, und dass es die direkte Pflicht eines jeden ist, sich dort nützlich zu machen, wo er sich am nützlichsten machen kann³

MARIE CURRIE

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Table of contents

Table of contents ...... iv

Abbreviations ...... vi

Acknowledgment ...... ix

List of schemes ...... xi

List of figures ...... xiv

List of tables ...... xvi

1 Introduction ...... 1

1.1 Hydrofunctionalization - An Overview ...... 2

1.2 Hydrochalcogenation (E = O, S, and Se) ...... 4

1.3 Hydrophosphanylation & Hydrophosphoranylation ...... 8

1.3.1 Early and late transition metal catalyzed H-P/ H-P(O) addition ...... 8

1.3.2 Lanthanoide-catalyzed H-P/H-P(O) addition ...... 14

1.3.3 Alkaline earth metal catalyzed H-P/H-P(O) addition ...... 17

1.4 Hydroamination ...... 22

1.4.1 Early and late transition metal-catalyzed hydroamination ...... 24

1.4.2 Lanthanoides and actinoides catalyzed hydroamination ...... 28

1.4.3 Alkaline metal-catalyzed hydroamination ...... 30

1.4.4 Alkaline earth metal-catalyzed hydroamination ...... 31

2 Motivation of this work ...... 36

3 Results and Discussion ...... 38

3.1 Synthesis and characterization of calcium and calciate complexes ...... 38

3.1.1 Synthesis and structural characterization of (thp)2Ca[N(SiMe3)2] [1] ...... 38

3.1.2 Synthesis and characterization of the calciate complex [K2Ca{N(H)Dipp}4]’ [2]...... 41 | v

3.2 Reactivity of [K2Ca{N(H)Dipp}4]’[2] in hydropentelation (N, P) reactions...... 44

3.2.1 Addition of primary arylamines ...... 44

3.2.2 Addition of secondary arylamines ...... 65

3.2.3 Addition of diphenylphosphane ...... 81

4 Summary and perspective (English version) ...... 95

5 Zusammenfassung (Deutsche Version) ...... 102

6 Experimental part ...... 109

6.1 Unpublished result ...... 110

6.1.1 Synthesis of N-(2,6-diisoprpylphenyl)-2,5-diphenylpyrrole [10] ...... 110

6.2 Published results...... 111

7 References ...... 112

8 Attachment ...... 121

9 Curriculum Vitae ...... 164

10 Selbstständigkeitserklärung ...... 169

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Abbreviations

Abbreviation Full-name Al Aluminum Au Gold AIBN ƍ-Azobis-(2-methylpropionitrile),2-(azo(1-cyano-1-ethylethyl)) methylpropane nitrile Ba Barium Ca Calcium CN coordination number Co Cobalt Cs Caesium Cy Cyclohexyl DME as solvent used 1,2-Dimethoxyethane Dme coordinated 1,2- Dimethoxyethane dppp Diphenylphosphanopropane dppe 1,2-Bis-(diphenylphosphano)ethane Et Ethyl

Et2O Diethylether Eu Europium Fe Iron Ga Gallium Gd Gadolinium Het Heteroatom Hg Mercury

Hf Hafnium HMDS hexamethyldisilazide i iso / ipso In Indium | vii i-Pr Isopropyl Ir Iridium J coupling constant L Ligand La Lanthanum Lu Lutetium M Metal symbol m Multiplet m meta Me Methyl Mes 2,4,6- Trimethylphenyl Mg Magnesium Nd Neodymium Ni Nickel NMR nuclear magnetic resonance O oxygen o ortho p para Ph Phenyl Pd Palladium Pt Platinum pka the negative base-10 logarithm of the acid dissociation constant of a solution. pmdta 111¶1¶¶1¶¶-Pentamethyldiethylentriamine Pr Praseodymium R, R`, R`` Alkyl Ru Ruthenium RT room temperature s singlet Sc Scandium Sr Strontium | viii

Sm Samarium t triplet Ta Tantalum t-Bu Tert-Butyl, 2,2 dimethylpropane-1-yl Tf Triflate Th Thorium THF as solvent tetrahydrofuran thf as coordinated solvent tetrahydrofuran THP as solvent tetrahydropyran thp as coordinated solvent tetrahydropyran TMEDA N,N,N',N'-Tetramethyl-ethylendiamine Ti Titanium Y Yttrium V Vanadium Yb Ytterbium Zr Zirconium į Chemical shift

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Acknowledgment

Foremost, I would like to express my sincere gratitude to my advisor Prof. Dr. Matthias Westerhausen for the continuous support of my Ph. D. study and research, for his patience, motivation, enthusiasm and immense knowledge. His guidance helped me in all the time of research and writing for the thesis. I cannot have imagined a better advisor and mentor for my Ph. D. study. I would like to thank him and his family for unlimited helpfulness when I had depressive moments due to my personal or private life. I am very much obliged to Westerhausen family for inviting me every Christmas and every Easter to their home and for cooking delicious American-German food, which eased me the homesickness.

Besides my advisor, I would like to thank I.A.E.S.T.E. organization in Syria and around the world. Through I.A.E.S.T.E., I could meet Prof. Westerhausen, personally in summer 2010 for a short-term practical course. As a result, I have started my Ph. D. program in his group.

I owe a debt of gratitude to Prof. Dr. Rainer Beckert for his patience, kindness and his time to explain me again what I did not understand in his organometallic lectures, due to my lack of skills in German language on that time.

I would like also to thank Prof. Dr. Jose Roberto Maia from the University of Viçosa, Brazil, for providing me the opportunity of a research stay for two months in the course of my studies. I thank Dr. Helmar Görls for the X-ray structural determinations of my compounds in this thesis.

Many thanks to individuals (technicians, co-workers, craftsmen and electricians) of the IAAC, especially those who measured NMR (especially Ms. Bärbel Rambach), IR and MS spectra and performed elemental analyses of my compounds.

During the time I spent at the Friedrich-Schiller-Universität (FSU) Jena, I was fortunate to interact with many great individuals of the workgroup of Prof. Matthias Westerhausen | x

(actual and former members, especially Dr. Tobias Kloubert, Dr. Jens Langer, Dr. Reinald Fischer, Dr. Carsten Glock, Mrs. Christine Agthe, members of the office 218, especially my best colleagues Steffen Ziemann and Stephan Härling who provided a good working atmosphere and helped me to correct and write the German part of this thesis).

Not to forget Mrs. Heike Müller, who was a very nice and friendly person. She helped me always when I asked her and never forget about my birthday date. May her soul rest in peace.

My sincere thanks goes to I.A.E.S.T.E., Germany, especially to local committee Jena. They are my small family in Jena (Sven, Sebastian, Uwe, Jan, Agnes, Marlen, Sophia, Larisa, Anka all of them). They shared with me each happy and unhappy moment and were ready to support me every time.

I owe a debt of gratitude to my friends Hassan and Laith for supporting and advise me specially on the writing time of my thesis.

I would like to thank each person who helped and motivated me to integrate with the German culture and to learn the German language especially my great flat mates (Paula and Christian) I will miss each moment we shared together.

I thank the Deutscher Akademischer Austausch Dienst (DAAD) for scholarship. Special thanks to Mrs. Birgit Kläs for advising and helping me every time I contacted her.

Last but not least, I would like to thank my whole family: Fatima and Mowafak, my lovely sisters Lina and Lama, the family of my great brother Feras, $ODD¶and Samsom (Sham). Without their encouragement, guidance and emotional support, none of this would have been possible. Special thanks to my cousin Maher Younis for great advices and support at the beginning of my Ph. D.

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List of schemes

Scheme 1.1: Catalyzed hydrofunctionalization reactions of alkene, alkyne, allene or diene...... 2 Scheme 1.2: Proposed catalytic cycles for intramolecular and intermolecular hydrofunctionalization reactions...... 3 Scheme 1.3: Formation of C-E bonds either via cross-coupling or via hydrofunctionalization reactions...... 4 Scheme 1.4: Examples of hydration and hydroalkoxylation process of alkynes, alkenes, allenes as well as hydroxycyclization and alkoxycyclization of enynes, respectively...... 5 Scheme 1.5: Mechanistic pathways for hydrothiolation of alkynes...... 6 Scheme 1.6: Product selectivity in hydrothiolation and hydroselenation of terminal alkynes...... 7 Scheme 1.7: Calcium-catalyzed hydrothiolation reactions...... 8 Scheme 1.8: Coordination of Phosphane and phosphane oxides to transition metals...... 9 Scheme 1.9:Markovnikov-selective Pd-catalyzed hydrophosphanylation of phenylacetylene...... 10 Scheme 1.10: Pd(Josiphos)-catalyzed asymmetric hydrophosphoranylation of norbornene...... 10 Scheme 1.11: Pd(Binaphos)-catalyzed asymmetric hydrophosphoranylation of styrene. .. 11 Scheme1.12: Cu-catalyzed hydrophosphanylation, hydrophosphoranylation and cross- coupling of a phosphane-borane and phenylacetylene...... 12 Scheme 1.13: Nickel-catalyzed hydrophosphoranylation of a propargyl alcohol...... 13 Scheme 1.14: Control of regiochemistry by metal catalyst in hydrophosphoranylation polymerization of diynes...... 13 Scheme 1.15: Iron catalyzed double hydrophosphanylation...... 14 Scheme 1.16: Lanthanoide-catalyzed the addition of phosphane to carbodiimides ...... 15 Scheme 1.17: Lanthanide-catalyzed hydrophosphanylation/cyclization of alkenyl- and alkynylphosphanes...... 16 Scheme 1.18: Ytterbium-catalyzed intermolecular hydrophosphanylation of alkynes...... 16

Scheme 1.19: Preparation of Mg[P(H)Ph]2(tmeda)...... 18 | xii

Scheme 1.20: Synthesis of alkaline earth phosphanides...... 18 Scheme 1.21: First example of the hydroamination reaction catalyzed by mercury chloride/ oxide...... 23 Scheme 1.22: Group IV catalyzed intramolecular and intermolecular hydroamination of alkenes and alkynes...... 25 Scheme 1.23: Organoactinides complexes catalyzed hydroamination reaction...... 28 Scheme 1.24: Lanthanocene-catalyzed intramolecular hydroamination of terminal aminoalkenes...... 29 Scheme 1.25: Diastereoselective cyclization of chiral aminoalkenes...... 29 Scheme 1.26: Synthesis ways of bis-[bis-(trimethylsilyl)amides] of the alkaline-earth metals...... 32 Scheme 1.27: Synthesis of heteroleptic calcium complexes by ligand exchange...... 33 Scheme 1.28: Intramolecular hydrophosphanylation, -phosphorylation and -amination reactions catalyzed by calcium-E-diketiminate complexes...... 34

Scheme 3.1: Synthesis of [(thp)2Ca{N(SiMe3)2}2]...... 39

Scheme 3.2: Synthesis of heterobimetallic [K2Ca{N(H)Dipp}4]’[2]...... 41 Scheme 3.3: The reaction of differently substituted anilines (a, b, c, d) with diphenylbutadiyne, in THF at room temperature...... 45 Scheme 3.4: Calciate-mediated hydroamination of diphenylbutadiyne with 2,6- diisopropylaniline in tetrahydrofuran yielding tetracyclic imine [5]...... 51 Scheme 3.5: Calciate-mediated hydroamination of diphenylbutadiyne with 2,4,6- trimethylaniline yielding N-mesityl-7-(E)-((mesitylimino)(phenyl)methyl)-2,3,6- triphenylcyclohepta-1,3,6-trienylamine [6]...... 53 Scheme 3.6: Complex [2] mediated hydroamination of diphenylbutadiyne with primary arylamines at high temperatures yielding N-Aryl-2,5-diphenyl-pyrroles...... 56 Scheme 3.7: Proposed mechanism of the complex [2] mediated hydroamination of diphenylbutadiyne with primary arylamines at high temperatures yielding N-aryl-2,5- diphenyl-pyrroles...... 59 Scheme 3.8: Proposed mechanisms of the s-block metal-mediated hydroamination of diphenylbutadiyne with primary arylamines at room temperature via a 1,2,4,6- | xiii cycloheptatetraene intermediate. The diphenylbutadiyne units are distinguished by the colors pink and green...... 62 Scheme 3.9: Addition of primary arylamines across diphenylbutadiyne under two different reaction conditions ((i) and (ii))...... 64 Scheme 3.10: Single hydroaminated diphenylbutadiyne...... 66 Scheme 3.11: Proposed catalytic cycle for the calcium-mediated hydroamination of diphenylbutadiyne (Ph = phenyl; R, R' = methyl aryl). Due to the fact that the exact composition of the catalytic species is unknown, the calcium catalyst is shown as

[LnCaNRR'] with L representing any Lewis base such as thf (solvent), amines and amides such as the anions NRR'- and N(H)Dipp-...... 71 Scheme 3.12: Synthesis of doubly hydroaminated diphenylbutadiyne...... 72 Scheme 3.13: Addition of secondary arylamines across diphenylbutadiyne under two different reaction conditions ((i) and (ii))...... 80 Scheme 3.14: Two-step synthesis of 1-(diphenylamino)-1,4-diphenyl-4- (diphenylphosphanyl)buta-1,3-diene using different calcium-based catalysts for the hydropentelation reactions...... 81 Scheme 3.15: Hydroamination and hydrophosphanylation of diphenylbutadiyne provided by K2[Ca{N(H)Dipp}4]...... 82 Scheme 3.16: Calcium-mediated synthesis of 1-(diphenylphosphanyl)-1,4-diphenyl-4-(N- methylanilino)buta-1,3-dienes (R= H [19], Me [20])...... 85 Scheme 3.17: The proposed catalytic cycles ...... 93 Scheme 3.18: Addition of diphenylphosphane to the singly hydroaminated molecules, [12], [13] and [*]. [*] is 1-diphenylamino-1,4-diphenylbut-1-ene-3-yne...... 94

Scheme 4.1: Proposed scheme for transamination of [(L)2Ca{N(SiMe3)2}]...... 101

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List of figures

Figure 1.1: Products of the ether cleavages for the calcium case...... 19 Figure 1.2: Selected group V metal catalysts for asymmetric hydroamination...... 25 Figure 1.3: Reaction pathways and product types in N-H addition reactions catalyzed by late transition metal complexes...... 27 Figure 1.4: cationic E-diketiminateo scandium complex...... 30 Figure 1.5: Heteroleptic complex of alkaline earth metals-E-diketiminate...... 34

Figure 3.1: Molecular structure and numbering scheme of [(thp)2Ca{N(SiMe3)2}2] [1]. .. 39 Figure 3.2: Section of the polymeric solid state structure of [2]...... 42 Figure 3.3: The investigated primary arylamines...... 44 1 Figure 3.4: H NMR resonances (400.08 MHz, [D8]THF, r.t) of the hydrogen atoms of the seven-membered ring of compound [3]...... 46 Figure 3.5: 1H NMR spectrum of the C-H fragments of the seven-membered ring of partly deuterated [3] (top) and with assignment to differently deuterated derivatives (bottom), for the CH group at į = 6.41 ppm...... 47 Figure 3.6: Molecular structures and numbering schemes of [3] (top) and [4] (bottom). .. 49 Figure 3.7: Molecular structure and numbering scheme of [5]...... 52 Figure 3.8: The 1H NMR resonances of the methyl substituents of the mesityl groups. .... 54 Figure 3.9: Molecular structure and numbering scheme of [6]...... 55 Figure 3.10: Molecular structure and numbering scheme of [9]...... 57 Figure 3.11: Molecular structure and numbering scheme of 1,2,5-triphenylpyrrole [11]. . 58 Figure 3.12: The investigated secondary arylamines...... 65 Figure 3.13: Molecular structure and numbering scheme of E-[12]...... 67 Figure 3.14: Molecular structure and numbering scheme of E-[13]...... 67 Figure 3.15: Molecular structure and numbering scheme of E-[14]...... 68 Figure 3.16: NMR spectroscopic monitoring of the second hydroamination of an E/Z- mixture of [12]...... 73 Figure 3.17: Time-dependent conversion of the singly hydroaminated compounds E-[12] and Z-[12] to the doubly hydroaminated isomer mixture [15] ...... 74 Figure 3.18: Molecular structure and numbering scheme of centrosymmetric E,E-[15]. .. 75 | xv

Figure 3.19: Molecular structure and numbering scheme of centrosymmetric Z,Z-[16]. ... 76 Figure 3.20: Molecular structure and numbering scheme of Z,Z-[17]...... 77 Figure 3.21: Molecular structure and numbering scheme of (E,E)-1-diphenylphosphanyl- 1,4-diphenyl-4-(diphenylamino)buta-1,3-diene (E,E-[18])...... 83 Figure 3.22: Molecular structure and numbering scheme of (E,Z)-1-diphenylphosphanyl- 1,4-diphenyl-4-(diphenylamino)buta-1,3-diene (E,Z-[18])...... 84 Figure 3.23: Molecular structure and numbering scheme of (E,Z)-1-( diphenylphosphanyl)- 1,4-diphenyl-4-(N-methyl-anilino)buta-1,3-diene (E,Z-[19])...... 86 Figure 3.24: : Molecular structure and numbering scheme of (E,Z)1-(diphenylphosphanyl)- 1,4-diphenyl-4-(N-methyl-tolylamino)buta-1,3-diene (E,Z-[20])...... 87

Figure 4.1: [(thp)2Ca{N(SiMe3)2}2] ([1])...... 95 Figure 4.2: Section of the polymeric structure of [2]...... 96 Figure 4.3: Hydroaminated diphenylbutadiyne by primary arylamines...... 98 Figure 4.4: Products of singly and doubly hydroaminated diphenylbutadiyne by secondary arylamines...... 100 Figure 4.5: Products of hydropentelation of diphenylbutadiyne by secondary amines and phosphane...... 101

Abbildung 5.1: [(thp)2Ca{N(SiMe3)2}2] ([1])...... 102 Abbildung 5.2: Ausschnitt der polymeren Struktur von [2]...... 103 Abbildung 5.3: Mit prämieren Aminen hydroaminiertes Diphenylbutadiin...... 105 Abbildung 5.4: Produkte von einfach und doppelt hydroaminiertem Diphenylbutadiin durch sekundäre Arylamine...... 107 Abbildung 5.5: Produkte von hydropentelation von Diphenylbutadiin von sekundären Aminen und Phosphan...... 108

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List of tables

Table 1: Calciumphosphanide/-amide-catalyzed HPPh2 addition to alkyne and alkene. ... 21 Table 2: Comparison of selected structural parameters of mononuclear calcium bis[bis(silyl)amides] of the type [(L)Ca{N(SiR3)2}2] [average values, bond lengths /pm and angles /°, CN(Ca) coordination number of calcium; dme 1,2-dimethoxyethane, thf, thp, t- BuIm N-tert-butylimidazole, tmeda tetramethylethylenediamine, py pyridine, dmap 4- dimethylaminopyridine, hmpa hexamethylphosphoric acid triamide]...... 40 Table 3: Comparison of selected bond lengths (pm) of 2-(tert-butyl)-6,7,10,11-tetraphenyl- 9H-cyclohepta[c]quinoline [3] and 2-(fluoro)-6,7,10,11-tetraphenyl-9H- cyclohepta[c]quinoline [4]...... 50 Table 4: Selected structural parameters (bond lengths [pm] and angles [deg.]) of the E- isomers E-[12], E-[13], and E-[14]...... 69 Table 5: Selected NMR data of the singly hydroaminated diphenylbutadiyne. The numbering scheme is identical with the molecular structures and can be seen in Figure 3.13, Figure 3.14 and Figure 3.15 ...... 70 Table 6: Selected structural parameters (bond lengths [pm] and angles [°]) of doubly hydroaminated diphenylbutadiyne...... 78 Table 7: Selected structural parameters of (E,E)-1-(diphenylphosphanyl)-1,4-diphenyl-4- (diphenylamino)buta-1,3-diene (E,E-[18]), (E,Z)-1-(diphenylphosphanyl)-1,4-diphenyl-4- (diphenylamino)buta-1,3-diene (E,Z-[18]), (Z,E)-1-(diphenylphosphanyl)-1,4-diphenyl-4- (N-methyl-anilino)buta-1,3-diene (Z,E-[19]) and (E,Z)1-(diphenylphosphanyl)-1,4- diphenyl-4-(N-methyl-tolylamino)buta-1,3-diene (E,Z-[20])...... 89 Table 8: Selected NMR data of the E,E and E,Z isomers of 1-(diphenylphosphanyl)-1,4- diphenyl-4-(diphenylamino)buta-1,3-diene ([18]), 1-(diphenylphosphanyl)-1,4-diphenyl-4- (N-methyl-anilino)buta-1,3-diene ([19]), and 1-(diphenylphosphanyl)-1,4-diphenyl-4-(N- methyl-tolylamino)-buta-1,3-diene ([20])...... 91

Introduction| 1

1 Introduction

Platinum had been reported as the first catalyst for industrial production of sulfuric acid in

1746 by J. ROEBUCK using the lead chamber process.[1] Since then, catalysts represent the corner stones of the development of new approaches in organic synthesis, medicinal chemistry, preparation of biologically active and pharmaceutical molecules, as well as in numerous applications related to material science and molecular electronics. Recent advances in green and sustainable chemistry emphasized the key role of waste-free chemicals production.[2] Increasing demand in complex molecular structures enforces implementation of sophisticated multistep synthetic procedures and further complicates the waste/product balance. So far most of the commodity chemicals remain to be produced by classical procedures, which are not considered as green.[3] The catalytic production of organic molecules is one of the most important applications of organometallic chemistry.[4] Hydrofunctionalization reactions open the way to form carbon-heteroatom bonds with environmentally friendly chemical transformations. Hydrofunctionalization of unsaturated organic molecules via direct addition of H-E (E = Se, S, O, P, N) to multiple bonds is an atom-economical addition reaction which does not produce wastes.[5] In view of the need of green and sustainable chemical procedures, the role of the metal catalysis is crucial to control the reaction, in particular with respect of regio-, stereo-, and enantioselectivity. To accomplish hydrofunctionalization reactions, various metal-based catalysts such as alkali metals (Li),[6] alkaline earth metals (Mg, Ca, Sr, and Ba),[7] group (III) transition metals Y[8] and Sc[9], lanthanoides Ln and actinoides An,[10] group (IV) transition metals Ti[11] and Zr[12], group (V) transition metals (e.g. V & Ta),[13] other transition metals like Fe,[14] Pd,[15] Hg,[16] Ru,[17] as well as post-transition metals like Al,[18] In,[19] and Bi[20] have been investigated.

Introduction| 2

1.1 Hydrofunctionalization - An Overview

Hydrofunctionalization is defined as an addition of a H-E (E = Se, S, O, P, N) bond across a multiple bond, in most cases a carbon-carbon multiple bond of an alkene, alkyne, allene or diene in the presence of proper catalyst (Scheme 1.1). Three classes of hydrofunctionalization that are termed as hydrochalcogenation (addition of H-Se, H-S or H- O), hydrophosphanylation (addition of H-P), hydrophosphoranylation (addition of H-P(O)), and hydroamination (addition of H-N) will be discussed.

Scheme 1.1: Catalyzed hydrofunctionalization reactions of alkene, alkyne, allene or diene.

Introduction| 3

Hydrofunctionalization occurs either via an intramolecular or an intermolecular manner as shown in Scheme 1.2.

Scheme 1.2: Proposed catalytic cycles for intramolecular and intermolecular hydrofunctionalization reactions.

To achieve the H-E addition, many factors play an important role:

1- Polarity of the H-E bond, electronegativity difference of H and E, determined by the Brönsted acidity of E. 2- The nature of the catalyst: electrocatalyst, organocatalyst, enzymes and biocatalyst, mono- or multinuclear catalyst, as well as naked catalyst or metal-free catalysts;[21] - + + [Ph2N ][Me4N ] and [Ph3C][Me4N ]. 3- Reaction parameters: homo- / heterogeneous conditions, temperature, pressure, and solvent.

2 Formation of carbon-heteroatom C(SP )-E bonds in vinyl compounds can take place via two powerful approaches; either via cross-coupling[22] or via hydrofunctionalization as shown in Scheme 1.3. However, the former usually also yields by-products and requires a multistep synthesis in order to form C-E bonds, whereas hydrofunctionalization is a single step addition process, using often commercially available and inexpensive starting materials.[23]

Introduction| 4

Scheme 1.3: Formation of C-E bonds either via cross-coupling or via hydrofunctionalization reactions.[3]

1.2 Hydrochalcogenation (E = O, S, and Se)

The addition of water or alcohols across unsaturated carbon-carbon bonds is one of the main synthetic methods to prepare ketones, ethers, epoxides, lactones, acetales and other oxygen containing compounds. Due to this fact many tireless efforts have aimed at improving the efficiency of the hydration and the hydroalkoxylation of alkynes,[24] alkenes[24a, 24e-g, 25], allenes[24a, 24e-g, 25] as well as hydroxycyclization and alkoxycyclization of enynes[26] using a variety of catalysts such as Au(I),[26c, 27] or Au(III)[28], Brönsted acids, Pt,[28a] Hg,[26c] Rh,[29] Ir, Ni,[30] Pd, and Ga[31] (Scheme 1.4).

Introduction| 5

Scheme 1.4: Examples of hydration and hydroalkoxylation process of alkynes, alkenes, allenes as well as hydroxycyclization and alkoxycyclization of enynes, respectively.

Equally important to the formation of carbon-oxygen bonds is the formation of carbon-sulfur bonds, due to the large number of various sulfur-containing natural and pharmaceutical products,[32] as well as the increasing demand of sulfur-containing ligands and chiral auxiliaries in synthetic chemistry.[33] Hence, thiols have been widely employed as sources of ligands for various transition metals. Generally, the reactions between thiols and transition metal complexes, which are mostly used in order to form the carbon-sulfur bonds, have two path ways: either the ligand-exchange reaction between high-valent transition metal n+2 complexes (M Lx) and thiols to give the complexes afford only thiolate ligands (RS- n+2 n M Lx-1), or the oxidative addition of thiols to low valent transition metals (M Ln) to give the corresponding transition metal complexes having both hydride and thiolate ligands as shown in Scheme 1.5.

Introduction| 6

Scheme 1.5: Mechanistic pathways for hydrothiolation of alkynes.

n+2 The reaction of the former complexes (RS-M Lx-1) with carbon-carbon unsaturated organic compounds such as alkynes may proceed via thiometallation, in which a relatively bulkier n+2 M Lx-1 is bonded at the terminal carbon of alkynes. In the reaction of the latter complexes n+2 (RS-M Lx-2-H) with alkynes both of the hydrometallation and thiometallation processes are possible. These processes proceed via syn-addition. An alternative pathway for the addition of thiols to alkynes involves coordination of alkynes to transition metals followed by nucleophilic addition of thiols (or thiolate anions) to the alkynes. These processes take place via anti-addition. By controlling these pathways, regio- and stereoselective hydrothiolation of alkynes is expected to be attained successfully. Hydrothiolation of alkynes was reported in 1949[34] with thioacetic acid and rediscovered in 2009.[35] Various catalysts have been applied to achieve the formation of sulfur-carbon bonds such as Pd, Ni, Pt, Rh,[36] indium(III) bromide,[37] AIBN,[38] Th, U,[39] Au,[40] and caesium carbonate.[41] It is worth here to mention that the hydrothiolation of terminal alkynes (Scheme 1.6) leads to many different products: Markovnikov-type adduct (A), Markovnikov addition and then double-bond-isomerization

Introduction| 7 product (B), anti-Markovnikov adduct (C), double hydrothiolation product (D), and bisthiolation product (F).

Scheme 1.6: Product selectivity in hydrothiolation and hydroselenation of terminal alkynes.[36, 42]

The addition of Se-H bonds to terminal alkynes matches the same results of hydrothiolation (Scheme 1.6). Generally, the formation of selenium-carbon bonds shows high similarity to the formation of sulfur-carbon bonds. Moreover, the oxidative addition of selenols to low-valent transition metals, ligand-exchange reactions between high-valent transition metal complexes and selenols and protonation processes of carbon-metal bonds are more efficient than the hydrothiolation. This difference in reactivity is attributed to the greater acidity of selenols (pKa = 5.9 {PhSeH}) compared to PhSH (pKa = 6.5), and the bond energy Se-H (73 kcal/mol) is smaller than that of S-H (87 kcal/mol).[43] The use of transition metal catalysts makes it possible to attain highly regio- and stereoselective syntheses of a variety of vinylic and allylic sulfides and selenides. These reactions are very useful in terms of the synthesis of organosulfur and selenium compounds and also the development of ELRDFWLYH FRPSRXQGV DQG QHZ PDWHULDOV )RU H[DPSOH ʌ-conjugated polymers including heteroatoms[44] are promising in material science and these research fields require highly selective methods for introduction of heteroatom groups involving oxygen, sulfur and selenium. Very recently, hydrothiolation reactions catalyzed by Lewis-acidic Ca complexes such as Ca(OTf2)2, Ca(NTf2)2 , Ca(NTf2)2/Bu4NPF6, Ca(OSO2C4F9)2 and Ca(ONf)2, have been reported and evaluated as efficient catalysts for bis-hydrothiolation of alkynes affording anti-Markovnikov dithioacetals (Scheme 1.7).[45]

Introduction| 8

Scheme 1.7: Calcium-catalyzed hydrothiolation reactions.[45]

1.3 Hydrophosphanylation & Hydrophosphoranylation

The chemistry of hydrophosphanylation and hydrophosphoranylation has grown explosively over the last decade, as it leads to organophosphane products despite the very small electronegativity difference between P, C, and H according to the diagonal relationship of C and P in the periodic table and similar ALLRED-ROCHOW electronegativities (P 2.06, C 2.5, H 2.20). Primary and secondary phosphanes can easily be deprotonated yielding phosphanides - R2P . These products can be widely employed in many research areas such as organic and organometallic syntheses. Furthermore, these reactions offer an efficient method to the syntheses of asymmetrically substituted phosphanes and phosphane oxides.[46]

1.3.1 Early and late transition metal catalyzed H-P/ H-P(O) addition

In each hydrofunctionalization reaction early and late transition metals,[47] which are stabilized by Lewis bases such as primary or secondary phosphanes or phosphane oxides, have been used as catalysts. Phosphane and phosphane oxide were attractive coligands for many reasons: (i) weak donors as Lewis and Brönsted bases compared to the hard donors oxygen and nitrogen, (ii) phosphane is a VWURQJHU DFLG ʌ-acidity is due to P-& ı  DQWL- bonding orbitals) than ammonia with the formal oxidation state (-III),[48] (iii) the lone pair of the P atom in phosphanes interacts with various soft transition metals leading to an active

Introduction| 9 metal complex (Scheme 1.8) which can be used as catalyst to accomplish the H-P/ H-P(O) addition across an unsaturated c-c bond.[49]

Scheme 1.8: Coordination of Phosphane and phosphane oxides to transition metals.[49]

The transition metal-based catalysts were extensively used to hydrophosphanylate or hydrophosphoranylate alkenes,[50] alkynes,[51] or other unsaturated backbones such as carbodiimides.[52] Due to the availability of d-orbitals which can easily and reversibly change their participation in bonding situation, intermediate reactions like the oxidative addition and the reductive elimination are supported[49b]. Moreover, the catalyst compounds which contain the d0 metal ions are the mediators for the activation of the strong multiple bonds such as carbon-carbon or carbon-oxygen multiple bonds[53]. For example, hydrophosphoranylation and hydrophosphanylation can be performed successfully with many transition metal-based catalysts[24d, 46b, 54]. Markovnikov or anti-Markovnikov selectivity in hydrophosphanylation of alkynes depend on the metal catalyst and the reaction conditions. The product distributions are thought to be controlled by the regioselectivity of insertion of an alkyne into an M-H or M-P bond. For example, Pd-catalyzed addition of

HP(OR)2(O) to a terminal alkyne was branched selectively, while HP(O)Ph2 preferentially gave linear products. However, a Pd(dppe) catalyst resulted in Markovnikov selectivity both for diphenylphosphane oxide[55] and the mixed substrate HP(Ph)(OEt)(O) (Scheme 1.9).

Introduction| 16

Scheme 1.17: Lanthanoide-catalyzed hydrophosphanylation/cyclization of alkenyl- and alkynylphosphanes.[70a] In comparison to the mechanism shown in Scheme 1.17, in which the hydrophosphanylation occurs via an intramolecular reaction, the lanthanides La, Sm, Y and Yb catalyze an intermolecular hydrophosphanylation of alkynes with the assistance of imines generating non-cyclic alkenylphosphanes (Scheme 1.18).[72]

Scheme 1.18: Ytterbium-catalyzed intermolecular hydrophosphanylation of alkynes.

In a recently reported hydrophosphanylation of butadiene with PH3 catalyzed by Cp2EuH, [73] the active species was proposed to be the phosphanido complex Cp2EuPH2. This complex can be formed in two ways, either by a single-step reaction, corresponding to a P-H activation of PH3 in the presence of Cp2EuH, or by a two-step reaction, involving a 1,3-butadiene insertion (mainly a 1,4- insertion) into the Eu-H bond followed by a P-H activation. P-C bond formation occurs by insertion of C-C unsaturated bonds of the butadiene into the Eu-P bond.[73] Based upon these findings, early transition metals, late transition metals and lanthanoides showed effectiveness and high productivity in catalyzing the H-P/H-P(O) addition across unsaturated systems (such as alkynes, alkenes or carbodiimides) to produce

Introduction| 17 the desired products showing remarkable regio-, chemo-, and stereoselectivities as well as asymmetrical and symmetrical structures. In addition to these advantages of the lanthanoides as well as the early and late transitions metals, the application of them has also disadvantages like the toxicity of lanthanides, the difficulty of isolating or obtaining most of them and the high price. Therefore, the attention of researchers was to find alternative metals that can give nearly the same advantages, but with less disadvantages. Obviously, the s-block metals (groups I and II) are excellent candidates to pursue these aims, especially the calcium and strontium whose ionic radii are similar to those of Yb2+[74] and Eu2+[75], respectively.

1.3.3 Alkaline earth metal catalyzed H-P/H-P(O) addition

Substitution of the expensive transition metals and lanthanoides by calcium would allow a more economic catalysis, even though lower turnover numbers (TON) would be achieved. This strategy is supported by the fact that ytterbium(II) shows far reaching similarities to the heavy alkaline earth metal cations. Ytterbium(II)-mediated hydrophosphoranylation of alkynes[76] does not involve a change of the oxidation state of Yb(II) and a similar reaction behavior of calcium(II) and ytterbium(II) compounds seems possible. Additionally, group II elements possess many features which made them attractive metals such as global abundance, low toxicity and costs. Thus, the use of group II metals in place of the rare elements is desirable. Chemically, group II elements have lower electronegativity, a stable oxidation state of (+2), lack of redox reactions and the presence of various coordination sites because of the large ionic radii. These properties allow the use of the alkaline earth metals (especially calcium) in numerous areas such as preparation of calciumphosphanide. In 1942 the first alkaline earth metal phosphanides were reported by LIGOUX.[77] LIGOUX prepared an alkaline earth-bis-(phosphanide) via reacting of calcium or strontium with phosphane in liquid ammonia. Twenty years later, Issleib and DEYLING[78] were able to synthesize magnesium-bis-(diphenylphosphanide) by the metalation reaction of diphenylmagnesium and diphenylphosphane. MASTHOFF et al. isolated the heteroleptic (Ph2P)CaCl in 1969 [79] through deprotonation of diphenylphosphane with (Ph3C)CaCl(thf)2. In 1987, HEY et [80] al. prepared the monomer Mg[P(H)Ph]2(tmeda) from the reaction of the polymer

Introduction| 18 magnesium-bis-(phenylphosphanide) with N,N,N',N'-tetramethylethylenediamine as shown in Scheme 1.19.

[80] Scheme 1.19: Preparation of Mg[P(H)Ph]2(tmeda).

In the 90s of the last century, WESTERHAUSEN isolated the complexes M-bis-

(bis[trimethylsilyl]phosphanide) (M = Ca, Sr, Ba) via deprotonation of HP(SiMe3)2 with M- bis-(bis[trimethylsilyl]amides) as depicted in Scheme 1.20.[81]

Scheme 1.20: Synthesis of alkaline earth phosphanides.[81a]

In 1998 KARSCH and REISKY reported the synthesis of the complex

[(Me2P)2C(SiMe3)]2Ca(thf)3 in which the central calcium has a coordination number of 7, because the calcium atom coordinates with both of the phosphane donors of the bidentate ligand.[82] Few years later IZOD et al. prepared a series of complexes of heavy alkaline earth [83] metals via the reaction the CaI2, SrI2 and BaI2 with K[P(CH{SiMe3}2)(C6H4-2-OMe)] , where this anionic ligand forms a chelate of a five- membered ring with the alkaline earth metal. Indeed, an ether cleavage often accompanies the formation of such complexes and

IZOD et al. showed that it is the case of the calcium as we can see in (Figure 1.1) while the ether cleavage was not observed in the cases of strontium and barium and the desired complexes could be isolated and characterized.[84]

Introduction| 19

Figure 1.1: Products of the ether cleavages for the calcium case.[83, 85]

A similar result to that reported by IZOD from the reaction between alkaline earth metal(II) iodide with K[P(CH{SiMe3}2)(C6H4-2-NMe2)] was obtained giving alkaline earth metal phosphanide complexes.[86] Shortly after that, Hill and coworkers[50] synthesized the heteroleptic calcium-diphenylphosphanide complex, [CH{C(Me)N-Dipp}2]Ca(PPh2)(thf), which is an intermediate in the hydrophosphanylation reactions catalyzed by the calcium E- i diketiminato [{HC(C(Me)N-2,6- -Pr2C6H3)2}Ca{N(SiMe3)2}(thf)] complex. Calcium-, barium- and strontium-diphenylphosphanide complexes were successfully synthesized and characterized by WESTERHAUSEN and coworkers.[85] They showed that calcium did not possess the capability to deprotonate the secondary phosphane (HPPh2). Therefore, two alternative reaction pathways allowed the synthesis of (thf)4Ca(PPh2)2, either the salt metathesis reaction of CaI2 with KPPh2 (due to the insolubility of KI in THF), or the metallation of diphenylphosphane with (thf)4Ca(Ph)PPh2 or (thf)2Ca[N(SiMe3)2]2. On the other hand, the deprotonation of HPP2 was accessible by metallic barium and strontium yielding barium and strontium-bis-(diphenylphosphanide) complexes. In 2007, HILL and coworkers[50] demonstrated that phosphaguanidines could be synthesized in high yield by the alkaline earth metal-catalyzed hydrophosphanylation of carbodiimides. A series of heavier alkaline earth metal-based catalysts including the heteroleptic calcium amide and the homoleptic alkaline earth amides [Ca{N(SiMe3)2}2]2, [Ca{N(SiMe3)2}2(thf)2],

[Sr{N(SiMe3)2}2(thf)2] and [Ba{N(SiMe3)2}2(thf)2] were applied to the hydrophosphanylation of carbodiimides with diphenylphosphane, di-p-tolylphosphane and dicyclohexylphosphane.[87] In 2012 the first alkaline earth metallocene complexes carrying 5 phosphanocyclopentadienyl ligands [M(L)x(Ș -C5H4PPh2)2] (M = Ca, Sr or Ba, L = THF or

Introduction| 20 dme and x= 1 or 2) have been prepared by redox transmetallation/ protolysis reactions.[88] Most of the calcium phosphanide complexes, alkaline earth-phosphanide complexes, calcium-E-diketiminate and its derivatives or calcium-E-diketamidinate[{2-

NC(Ph)NArC6H4CHNAr}Ca{N(SiMe3)2}(thf)]x, were applied as catalysts to accomplish hydrophosphanylation and hydrophosphoranylation reactions.[7d, 89] In Table 1 we can see selected examples of calcium-phosphanide/-amide complexes catalyzing H-PPh2 addition to alkynes and alkenes.

Introduction| 22

1.4 Hydroamination

The addition of an amine N-H moiety across an unsaturated carbon-carbon linkage of alkenes, allenes or alkynes is termed as hydroamination. Formation of amides is a fundamental reaction in organic syntheses.[91] The importance of amides in biology, chemistry and technology is well recognized due to the presence of this functionality in many natural products, proteins, pharmaceuticals, and therapeutic drugs.[92] Organonitrogen compounds which are accessible via hydroamination reactions are widely encountered in industrial and natural products or synthetic drugs such as: Bactericides, herbicides, corrosion inhibitors, extraction agents, intermediates in the synthesis of penicillin, softening agents, wetting agents, dye fixers, asphalt emulsifiers, pigment dispersing agents, petroleum additives, a polymer in paper making, textile finishing.[93] Recently, it is reported that during the course of drug discovery almost 16% of all reported reactions are amide bond formation and over 50% of all drug candidates contain at least one amide bond functionality.[93] For example monomprine is one of the first natural products that became accessible by synthetic steps including a hydroamination step.[94] Moreover, the Chinese folk medicine uses organonitrogen compounds to treat cold, stomachache and rheumatism by extracts of the plant Carduus crispus. After extraction and characterization, the active materials of this plant were also synthesized in order to be used as inhibitors for some growing human cancer cells.[95] Indeed, hydroamination was one of the synthetic steps toward these active components of Carduus crispus.[95] Historically, hydroamination has got great attention owing to its important applications in various areas as mentioned above. In 1936 KOZLOV reported the first hydroamination reaction and the homogeneous catalyst mercury(II) chloride was used. KOZLOV described that the addition of aniline to acetylene in the presence of mercury(II) chloride leads to N-[(1E)-ethylidene]-aniline (Scheme 1.21, top).[96]

Three years later, LORITSCH et al developed a mercury oxide catalyzed hydroamination of terminal and internal alkynes with aniline (Scheme 1.21, bottom).[97]

Introduction| 23

Scheme 1.21: First example of the hydroamination reaction catalyzed by mercury chloride/ oxide.[96-97]

Hydroamination has been examined with a variety of primary and secondary amines, cyclic and acyclic amines as well as anilines with diverse steric and electronic substituents. In addition to the type of the amine, the nature of the catalyst (homo-/heteroleptic) and the unsaturated system also influence the selectivity (regio-, chemo-, stereo-) of the reaction as well as the product symmetry (symmetrical or asymmetrical). The need of a catalyst is owing to the repulsive interaction between the amine lone pair and the electron-density of the unsaturated bond that makes the hydroamination a kinetically unfavorable process. Vastly, numerous catalysts have been prepared applying different methods such as: (i) direct metallation, (ii) salt metathesis, (iii) deprotonation (acid-base reaction). Catalysts based on metals throughout the periodic table have been reported using early and late transition metals,[98] lanthanoides and actinoides,[70b, 99] alkaline earth metals[49b, 87], and alkali metals which have been reported by WEGLER and PIEPER since 70 years.[100] Noteworthy hydroamination reaction can also be substantially accelerated by addition of catalytic amounts of acids [101] or bases [6, 102]. Furthermore, the presence of acid not only accelerates the reaction, but also it did enhance the enantioselectivity. Recently, DONG and coworkers have shown that the presence of m-xylylic acid leads to an enantioselectivity up to 90% ee.[103] The unsaturated substrates that have been investigated for intermolecular hydroamination reactions include alkenes, dienes, alkynes and allenes. For intramolecular hydroamination, various aminoalkenes and aminoalkynes have been examined.

Introduction| 24

1.4.1 Early and late transition metal-catalyzed hydroamination

Strikingly upon, hydroamination reactions have to overcome certain challenges such as unfavorable entropic effects, electrostatic repulsion between a strongly Lewis basic amine and an electron-rich multiple bond and lack of significant exothermic reaction enthalpy. Due to these facts, several strategies have been developed to support the addition of N-H functionalities to the C-C multiple bonds. On the one hand, activation of alkenes and alkynes often succeeds in the vicinity of late transition metals by back-donation of charge from the metal-centered GRUELWDOVLQWRʌ RUELWDOVRIWKHDONHQHVDQGDON\QHVLQDJUHHPHQWZLWKWKH Dewar-Chatt-Duncanson model.[104] On the other hand, the amines can be activated by oxidative addition to transition-metal complexes or by deprotonation and formation of the - - much more aggressive and nucleophilic amides (R2N ) or even imides (RN2 ) of early transition metals or s-block metals. The disadvantageous entropy value can be minimized by an intramolecular hydroamination reaction, leading to cyclic amines or imines. Organoreset complexes of early transition metals such as group IV have been used to catalyze the inter- and intramolecular hydroamination reactions. The application of group IV metal complexes to intramolecular alkene hydroamination has become a vibrant and quickly developing field since the first reports have been published.[12, 105] Comparing the complexes of group IV elements and those of the rare earth and alkaline earth metals will lead to several important features of these catalysts: (i) the reactivity of group IV metal catalysts remains low, thus demanding higher catalyst loading and temperatures, which often leads to side reactions. (ii) Generally catalysts of group IV are restricted to gem-dialkyl-activated substrates and terminal alkene moieties. (iii) Only few systems are able to approach cyclization of both primary and secondary aminoalkenes and aminoalkynes.[7b, 106] Homoleptic amides of titanium[105b] and zirconium[107] have been used as catalysts for the cyclization of aminoalkenes (Scheme 1.22, top). In numerous cases, titanium catalysts are significantly more reactive than zirconium or hafnium catalysts not only in intramolecular hydroamination of aminoalkenes, but also intermolecular hydroamination of asymmetric, symmetric, internal and terminal alkynes as we can see on the bottom of Scheme 1.22.

Introduction| 25

Scheme 1.22: Group IV catalyzed intramolecular and intermolecular hydroamination of alkenes and alkynes.[105b, 106b, 107-108]

Group V metal complexes have been also used to catalyze hydroamination reactions as recently was reported by HULTZSCH and coworkers.[109] They could show that group V complexes are more active than group IV to obtain the asymmetric products which are results from hydroamination reactions of aminoalkenes as well as alkenes, which is catalyzed by binaphtholate tantalum and niobium derivation (Figure 1.2, left).[109] The chiral complex vanadium(IV)-bis-(amidate) (Figure 1.2, right) also showed appreciable catalytic activity and enantioselectivity for the asymmetric hydroamination/cyclization whereas the corresponding tantalum complex was not an efficient catalyst.[13]

Figure 1.2: Selected group V metal catalysts for asymmetric hydroamination.[13, 109]

Complexes of late transition metals are highly desirable for catalytic hydroamination due to their low reactivity toward oxygen-containing functional groups. Many different catalyst systems of the late transition metals have been disclosed and developed within the past

Introduction| 26 decade and showed high efficiency. Figure 1.3 represents an overview of various late transition metal-based catalysts. Gold[110] and silver[111] complexes have been deeply and intensively studied for the hydroamination of unsaturated systems such as alkenes, allenes, and alkynes. Silver and gold catalysts are often combined to catalyze hydroamination reactions, whereas silver salts with non-coordinating anions are used to abstract halide ions from gold catalyst and thereby to enhance its Lewis acidity. In addition, gold complexes are of particular efficiency for catalyzing the asymmetric addition reactions (for example, intermolecular hydroamination of 1,3-dienes and allenes). Furthermore, gold catalysts have been reported to give extremely high turnover numbers up to 9500.[112] Palladium complexes are intensively used in both types of hydroamination reactions to hydroaminate alkynes or aminoalkynes. For instance, intramolecular hydroaminations of aminoalkynes represent an advantageous strategy to synthesize indoles.[113] Additionally, palladium is the ideal metal for C-C coupling / intramolecular hydroaminations. Nonetheless, the intermediate alkyl- palladium tends to undergo E-hydride eliminations and hence limits the use of Pd in intermolecular hydroaminations of alkenes. However, this fact opens new opportunities for oxidative amination processes. In contrast, platinum complexes have low tendency toward E-hydride eliminations. Therefore, they show high efficiency to accomplish intra- and intermolecular hydroamination of alkynes and alkenes.[114] In relation to late transition metal-catalyzed hydroamination reactions, rhodium complexes have been reported as excellent active catalysts in intermolecular hydroamination of not only alkynes, but also alkenes in addition to their high selectivity for anti-Markovnikov addition products.[115] In assistance of chiral 2-dialkylphosphano-2´-alkoxy-1,1-binaphthyl ligands, Rh allows an efficient synthesis of various chiral amines via asymmetric cyclization of aminoalkenes.[116] Similar to Rh, iridium complexes are active in both types of hydroamination of terminal alkynes and alkenes with anilines and heteroaromatic amines, but in counter to Rh, hydroamination reactions catalyzed by Ir usually lead to Markovnikov addition products.[117] Moreover, chiral Ir complexes have been also reported as efficient catalysts to accomplish the asymmetric intermolecular hydroamination of alkenes with heteroaromatic amines.[118] Ru catalysts are basic catalysts for the hydroamination of terminal alkynes with highly regio- and stereoselectivity. These catalysts also show high efficiency in asymmetric intermolecular hydroaminations of alkenes.[119] As rival of ruthenium, Re catalysts have been

Introduction| 28

1.4.2 Lanthanoides and actinoides catalyzed hydroamination

Similar to the addition of H-P moieties across unsaturated systems, rare earth metal complexes have proven to be very active and efficient catalysts for H-N addition across unsaturated linkages. In comparison with organolanthanoide[123] catalysts, only a limited number of organoactinoide catalysts has been investigated for inter-/intramolecular hydroamination reactions.[124] Although organoactinide catalysts showed in many cases higher efficiency and wider application for a broad range of substrates [124a-c] than the corresponding organolanthanoide catalysts, their use is limited because of many factors related to the costs, lack of global abundance and health risks as well as difficulties of dealing with these metals. For example, the thorium and uranium complexes (Scheme 1.23, bottom right) show higher activity to catalyze the intramolecular hydroamination reaction than the corresponding organolanthanoide complexes. Also one of the important actinoide complexes, which is used as catalyst for the hydroamination of aminoalkenes, is the ferrocene diamido-uranium complex as shown in Scheme 1.23, bottom left.

Scheme 1.23: Organoactinides complexes catalyzed hydroamination reaction.[124a-c]

Despite the difficulties in intermolecular hydroamination reactions catalyzed by organolanthanides complexes that are caused by the inefficient competition between strongly binding amines and weakly binding alkenes for available coordination sites at the catalytically active center, some examples have been reported.[125] On the other hand complexes of organolanthanoides are very efficiently in catalyzing intramolecular

Introduction| 30

[131] [99c, 99d, 129] [128a] Sm{N(SiMe3)2}2 or chelating diamides, diamidoalkylamine complexes, amino troponiminato,[132] bis-(phosphanimino)- methanide,[133] salicylaldiminato[9, 134] and E-diketiminate. Complexes of E-diketiminate can be synthesized with good yields by the transmetallation reaction as has been reported for samarium and gadolinium E-diketiminate complexes by DREES et al..[135] Similarly complexes of cesium, samarium and neodymium

E-diketiminate were described by HITCHCOCK et al..[136] The lanthanide complexes with E- diketiminate ion could also be chargeable systems in special cases, for example the E- diketiminato scandium complex, has been reported by LAUTERWASSER et al., is cationic (Figure1.4).[9] This cationic system did show improved catalytic activity over its neutral congener.

Figure 1.4: cationic E-diketiminateo scandium complex.

1.4.3 Alkaline metal-catalyzed hydroamination

Alkaline metals such as Li, Na, k and Cs have been used as strong base or strong electropositive metals to catalyze hydroamination reactions for a long time.[6a, 102] Lithium diisopropylamide (LDA), lithium hexamethyldisilazide (LiHMDS), lithium diethylamide- tetramethylethylendiamine (LiNEt2-TMEDA) and lithium tetramethylpiperidide (LiTMP),[137] as well as n-BuLi[138] and sec-BuLi[138c] are widely employed to deprotonate various substrates and to catalyze inter-/intramolecular hydroamination reactions. Na metal has been reported to mediate hydroamination reactions, like the addition of aniline to 1,3- butadiene at high temperature,[139] while the use of organosodium complexes such as sodium

Introduction| 31

naphthalenide (Na2Naph) or sodium ethoxide (NaOEt) as a catalyst were sufficient to accomplish hydroamination reactions at room temperature.[140] To the best of our knowledge pure potassium has never been used successfully as a catalyst for hydroamination reactions, but organopotassium compounds have been studied. For example, KO-t-Bu has been used as a catalyst for the addition of primary and secondary amines to unsaturated systems.[141] In [142] addition, K2CO3 has also been used for the same desires. Caesium hydroxide

(CsOH.H2O) solution has been reported as a catalyst for hydroamination reactions in the beginning of this century.[143] However, this compound is not commonly used as a catalyst because the extraction process of caesium compounds is very expensive and these compounds behave very much like rubidium hydroxide and potassium hydroxide even though they are more reactive. Moreover, organo alkali metal compounds have been employed to enhance the activity and the efficiency of other transition metal catalytic [144] [143] systems. For example n-BuLi and CsNH2/RbNH2 have been used as cocatalyst to promote Co[acac].

1.4.4 Alkaline earth metal-catalyzed hydroamination

Although organolanthanoide catalysts possess surpassed reactivity in inter-/intramolecular hydroamination, the development of more robust, environmentally benign and readily available catalysts remains an important target. Due to the fact that many of the lanthanoides are similar to alkaline earth metals, for example Ca and Sr to Yb(II)[74] and Eu(II),[75] respectively. There is a growing interest in the syntheses and characterization of group II- amides due to their utility as a precursor for the synthesis of a spectrum of group II compounds [7d, 52b, 145] and also as versatile catalysts in various organic transformations.[7d, 50,

146] This interest has been begun in the 60s of last century when JUZA et al. recognized that [147] strontium and barium in liquid ammonia can form the corresponding amides, Sr(NH2)2 [148] and Ba(NH2)2 within some days, while calcium required more than one month to react with liquid ammonia[147] and the synthesis of magnesium-bis-amide was successful via reacting magnesium nitride with ammonia under harsh conditions (350 °C, 10 bar).[149] A few years later UTKE and SANDERSON[150] were able to synthesize many calcium amide complexes, which are sensitive to the air and moisture as well as poorly soluble and pyrophoric, via reacting different amines with the solvated calcium in ammonia. Metalation

Introduction| 33 properties of early transition metals and divalent lanthanides (d-orbital participation, catalytic activity). However, one major problem in studying the catalytic features of Ca-compounds is related to the solubility and therefore many efforts have been made in order to enhance the solubility, but this leads to decreased reactivity. As an example, calcium- bis[bis(trimethylsilyl)amides] are soluble in common organic solvents, but the reactive Ca- N bonds are effectively shielded and the reactivity is reduced.[81a] Large and/or multidentate ligands can circumvent this solubility issue. It has been found that heteroleptic calcium ȕ- diketiminate complexes with bulky substituent complexes are highly soluble and possess sufficient reactivity to accomplish the intramolecular hydroamination of aminoalkenes. The chemistry of the ligand ȕ-diketiminate has started in the middle WRODWH¶VDVKRPROHSWLF complexes of Co, Ni, Cu, Zn[155] and lanthanoide elements.[135b, 136, 156] Based on the facts that there are direct parallels between the chemical behavior of the heavier alkaline earth metals and lanthanides, L (L = CH(CMe-2,6-iPr2C6H3N)2) has stabilized the first example [157] of a monomeric magnesium(I) compound [LMg]2 with a Mg-Mg bond. Furthermore, at the beginning of this century, HARDER represents another resemblance between the chemistry of alkaline earth and early d- and f-block metals by his observation of C-H activation in a benzylcalcium complex which acted as an initiator for the living syndiotactic polymerization of styrene.[158] Thus, the success of the E-diketiminate ligand in polymerization catalysis[159] promoted their use in heteroleptic benzylcalcium initiators. HARDER showed that these heteroleptic alkaline earth complexes can be prepared by ligand-exchange between two homoleptic compounds with the consideration of the steric and electronic effects as well as the thermodynamic and kinetic effects as shown in Scheme 1.27.[158a]

Scheme 1.27: Synthesis of heteroleptic calcium complexes by ligand exchange. [158a]

Introduction| 35

In consideration of the atomic radii of alkaline earth metals and their similarity to rare earth PHWDOVUDGLL¶VDQGLQRUGHUWRWXQHWKHFDWDO\WLFSHUIRUPDQFHDQGUHDFWLRQSDWWHUQVRIWKH complexes of these highly electropositive metals, in 2012 CUI and coworkers reported the synthesis of calcium-E-diketamidinate [{2-NC(Ph)NArC6H4CHNAr}Ca{N(SiMe3)2}(thf)] and the corresponding Yb complex that are stabilized by a tridentate ligand. These complexes showed higher efficiency and selectivity than the calcium-E-diketiminate in the intermolecular hydrophosphanylation reaction (Table 1).[90] WESTERHAUSEN and coworkers reported earlier that calcium-bis(diphenylphosphanide) acts as a catalyst to accomplish hydrophosphanylation reactions of diphenylphosphane across the &Ł& triple bonds of different substituted butadiene backbones (Table 1).[51b] Similarly, calcium-bis- (diphenylamide) has been synthesized, characterized and used as catalyst to accomplish the addition of diphenylamine across &Ł&triple bond of diphenylbutadiyne. It has been found that Ca(NPh2)2 is less active than Ca(PPh2)2 and not efficient enough to accomplish the amine addition. Hence, a reactivity enhancement research has been carried out and series of ³aWH´FRPSOH[HVFRXOGEHV\QWKHVL]HGYLDVDOWPHWDWKHVLVUHDFWLRQs, where excess amounts of potassium amide salts are necessary for the formation of the calciate complexes

[K2Ca(NRAr)4]’ (R= H, Ph, Me. Ar = Dipp, Ph) that were successfully synthesized and characterized.[162]

Motivation of this work| 36

2 Motivation of this work

In industry, several important factors must be considered in determining any catalytic process such as the costs of substrates, atom efficiency and process economics. Despite the fact that hydroamination or hydrophosphanylation reactions proceed with 100% atom economy (without waste production) and the unsaturated carbon linkages, amines and phosphanes are most often economically advantageous compared to other starting materials for certain product, the main cost determining issue for these reactions is the catalyst cost. Calcium represents one of the most attractive metal with respect to the future applications in chemistry due to the properties such as: x Abundance (the fifth most frequenWHOHPHQWLQWKHHDUWK¶VFUXVWZLWKwt. %).[49b] x Inexpensive compared to other metals like platinum or palladium (10¼SHUPROYV~ ¼SHUPRO  x The non-toxicity of calcium containing solutions (regardless of its concentration) allows diverse applications in medicine and biomedicine as well as in the preparation of materials for surgery, orthopedics, and tissue engineering. x Calcium has lower electronegativity compared to rare earth metals and its stable oxidation state of +II. x Ability of Ca to be coordinated to various ligands due to its large ionic radius (1.06 Å). x The intermediate position in the periodic table between typical s-block metals and early transition metals makes calcium a fascinating element because it combines d- orbital participation in bonding situations and catalytic activity with very heteropolar bonds of an enormous reactivity.

In this research work diphenylbutadiyne will be the only alkyne used here despite the fact WKDWDON\QHVKDYHPRUHʌ-electrons than alkenes, which could be expected to increase the electrostatic repulsion of the nucleophile where metal-catalyzed addition reactions across CŁC triple bonds are much easier to occur than those across C-C double bonds. This can be H[SODLQHGE\WKHIRUPDWLRQRIVXEVWDQWLDOO\ZHDNHUʌ-bonds between the metal center of most catalysts and alkynes as compared to alkenes. The intermediate strength of the interaction

Motivation of this work| 37 between the alkyne and the catalyst allows activating the CŁC triple bond toward QXFOHRSKLOLFDWWDFNZLWKRXWLQKLELWLQJWKHUHDFWLRQE\DVWURQJʌ-coordination to the metal center. Furthermore, alkynes are sterically less hindered toward attack of the nucleophile. In addition, hydroamination of alkynes yields either imines or enamines, which are useful reagents for a wide variety of organic transformations. The aims of this thesis are summarized by the following points: (1) Synthesis and characterization of calcium and calciate catalysts which are capable to accomplish the addition of amines or phosphanes across the CŁC triple bonds of diphenylbutadiyne.

(2) Application of the synthesized catalyst to mediate the hydroamination of diphenylbutadiyne by primary amines.

(3) Hydroamination of diphenylbutadiyne by secondary amines and optimization of the regioselectivity.

(4) Studying the reactivity of the prepared catalysts toward the addition of diphenylphosphane across the singly hydroaminated diphenylbutadiyne.

Results and Discussion| 38

3 Results and Discussion

In this section all the achievements will be shown and scientifically discussed, starting from the synthesis of the efficient catalyst, followed by the reactivity study of these catalysts in the addition of various of primary and secondary arylamines to diphenylbutadiyne as well as the addition of diphenylphosphane to the singly hydroaminated products. 3.1 Synthesis and characterization of calcium and calciate complexes

3.1.1 Synthesis and structural characterization of (thp)2Ca[N(SiMe3)2] [1] At the beginning of this work we were focusing in preparation of new calcium complexes which is enough active to mediate the addition of amines and phosphanes across a diyne system. Due to the tremendous importance of [Ca{N(SiMe3)2}2] as thf adduct in organocalcium chemistry, we applied it as catalyst to accomplish the addition of primary amine across diphenylbutadiyne, but the reactivity of this catalyst was not high enough. However, tetrahydrofuran exhibits ring strain and Į-acidic hydrogen atoms and hence, ether cleavage can occur quite easily during metal-organic transformations. According to the fact, that tetrahydropyran (thp) is a weaker and bulkier base than thf, we expected that a slight enhancement in the reactivity could be gained. Therefore, we investigated the tetrahydropyran adduct of [Ca{N(SiMe3)2}2]. In order to obtain halide-free

[(thp)2Ca{N(SiMe3)2}2] [1], we have chosen the transmetalation of freshly distilled

Sn[N{SiMe3}2]2 with calcium granules according to Scheme 3.1. During this heterogeneous reaction the color of the solution turned reddish brown. After filtration, removal of the solvent in vacuum and recrystallization of the residue from n-hexane, pure [1] was isolated as shown in Figure 3.1. Other preparative routes also seem to be feasible. However, considering the recent report from JOHANS et al.[163] the salt-metathesis reaction can yield

[Ca{N(SiMe3)2}2] that is contaminated with KN(SiMe3)2.

Results and Discussion| 39

[164] Scheme 3.1: Synthesis of [(thp)2Ca{N(SiMe3)2}2].

Figure 3.1: Molecular structure and numbering scheme of [(thp)2Ca{N(SiMe3)2}2] [1]. The ellipsoids represent a probability of 40 %, H atoms are neglected for clarity reasons. Symmetry-related atoms (-x+1, y, -] DUHPDUNHGZLWKWKHOHWWHU³$´6HOHFWHGERQG lengths (pm): Ca1-N1 231.08(11), Ca1-O1 240.23(9), N1-Si1 168.84(11), N1-Si2 168.95(12), Ca1···C6 318.16(17), Ca1···Si1 346.56(4), Ca1···Si2 334.39(4); angles (deg.): N1-Ca1-N1A 119.43(6), N1-Ca1-O1 94.31(4), N1-Ca1-O1A 134.86(4), O1-Ca1-O1A 78.57(5), Ca1-N1-Si1 119.31(6), Ca1-N1-Si2 112.49(5), Si1-N1-Si2 128.19(7). The tetra-coordinate metal atom is in a severely distorted tetrahedral coordination sphere with a large N1-Ca1-N1A angle of 119.4°. The nitrogen atoms are in distorted trigonal planar environments with an average N-Si bond of 168.9 pm. This short bond is characteristic for bis(trimethylsilyl)amides bound at electropositive s-block metals[165] because the hyperconjugation of the negative charge from the pz 1  RUELWDO LQWR ı 6L-C) orbitals strengthens the N-Si bonds. The bulkiness of the trimethylsilyl groups enforces a large Si1- N1-Si2 bond angle. In order to evaluate structural characteristics, mononuclear calcium- bis[bis(silyl)amides] are summarized in Table 2. The compounds are arranged according to the coordination number of the calcium atom [CN(Ca)] and within these groups according to the Ca-N distances. It is obvious that bulkier silyl substituents lead to elongated Ca-N bonds which vary between 227 and 239 pm. The Ca-L distances (the donor atoms are given in brackets) strongly depend on the donor base because the atomic radii decrease from C over N to O. However, the major influence of these co-ligands on the Ca-N bond lengths seems to be of steric nature. Even the coordination number of calcium plays a minor role as

Results and Discussion| 40 can be seen from the complexes with three- and five-coordinate alkaline earth metal centers showing Ca-N values well within the range for adducts with tetra-coordinate calcium atoms. Table 2: Comparison of selected structural parameters of mononuclear calcium bis[bis(silyl)amides] of the type [(L)Ca{N(SiR3)2}2] [average values, bond lengths /pm and angles /°, CN(Ca) coordination number of calcium; dme 1,2-dimethoxyethane, thf, thp, t- BuIm N-tert-butylimidazole, tmeda tetramethylethylenediamine, py pyridine, dmap 4- dimethylaminopyridine, hmpa hexamethylphosphoric acid triamide].

L NSiR3 CN(Ca) Ca-N Ca-L /pm N-Ca-N/° Ref. /pm

NHC-1 N(SiMe3)2 3 229.0 259.8 (C) 125.4 [166] NHC-2 N(SiMe3)2 3 230.3 262.9 (C) 124.5 [166] thf N(SiMe3)(SiPh2t-Bu) 3 232.3 238.2 (O) 134.6 [167] dme N(SiMe3)2 4 227.1 239.7 (O) 123.6 [168] 2 thf N(SiMe3)2 4 230.2 237.7 (O) 121.3 [169] 2 thp N(SiMe3)2 4 231.2 240.2 (O) 119.4 [164] 1 tmeda N(SiMe3)2 4 231.5 259.2 (N) 121.8 [170] 2 t-BuIm N(SiMe3)2 4 232.5 246.4 (N) 123.3 [171] 2 Ph3PO N(SiMe3)2 4 233.7 226.5 (O) 129.4 [166] 2 py N(SiMe3)(SiMe2t- 4 235.3 253.7 (N) 125.3 [167] Bu) a 2 thf N(SiMe3)(SiPh3) 4 236.0 237.3 (O) 146.6 [167] 2 dmap N(SiMe3)(SiMe2tBu) 4 236.7 249.8 (N) 122.3 [167] 2 hmpa N(SiMe3)(SiMe2tBu) 4 239.0 228.0 (O) 125.2 [167] b 3 thf N(SiMe2CH2)2 5 233.6 240.2 (O) 136.8 [153b] a) Coordination number 4+2 due to two additional agostic interactions to trimethylsilyl groups; b) trigonal bipyramidal environment of Ca with the amido ligands in equatorial positions.

The enhancement in reactivity which have been tendered by replacement of the donor ligand L (thp, thf) was also not sufficient to accomplish the hydroamination reactions. This work was published in 2013.[164]

Results and Discussion| 41

3.1.2 Synthesis and characterization of the calciate complex [K2Ca{N(H)Dipp}4]’ [2].

The fact that monometallic calcium-bis(amide) does not mediate the hydroamination reactions, raises the question of the cooperation of potassium and calcium in the catalyst system. MULVEY and his coworkers, reported that mixed alkali-metal-magnesium alkylamides tend to form inverse crowns which react as highly reactive metalation reagents.[172] Hence, the work here focused on the enhancement of our calcium catalyst via the formation of heterobimetallic s-block metal amides [K2Ca{N(H)Dipp}4]’which can only be prepared in presence of excess potassium amide KNHDipp, while the stoichiometric reactions led to homometallic complexes such as b, c, d, e, f, g, and h complexes as shown in Scheme 3.2.

Scheme 3.2: Synthesis of heterobimetallic [K2Ca{N(H)Dipp}4]’ [2].

The calciate complex [2] has been precipitated from a THF solution as a solvent-free coordination polymer. Mixed metal amide complexes often behave differently than the homometallic congeners. However, a comparison on the basis of NMR parameters of b, c, d, e, f, g and [2] showed us similarities between these complexes with respect to the chemical shifts in the 1H and 13C{1H} NMR spectra. These similarities can be explained by the dissociation of these complexes and dynamic behavior that is fast on the NMR time scale. These parameters verify that complex [2] breaks up its polymeric structure in the solution, which also explains the good solubility in common organic donor solvents. A section of the

Results and Discussion| 42 polymeric solid state structure of [2] including the heterobimetallic amide with a ratio of 2:1 for K:Ca is shown in Figure 3.2. It is obvious that the less electropositive metal Ca binds to the amido-ligand, forming a calciate, while the more electropositive metal K represents the counter cation.

Figure 3.2: Section of the polymeric solid state structure of [2]. The ellipsoids represent a probability of 40 %, H atoms are neglected for clarity. The letters A (-x, y, -z + 0.5) and B (-x, -y + 2, -z) characterize symmetry-related atoms. Selected bond lengths (pm): Ca1-N1 232.9(3), Ca1-N2 239.3(3), K1-N1 294.1(3), K1-C1 292.9(3), K1-N2 287.2(3), K1-C13B 335.0(3), K1-C14B 324.1(3), K1-C15B 308.8(3), K1-C16B 304.2(4), K1-C17B 312.1(3), K1-C18B 327.4(3), N1-1 137.9(4), N2-C13 137.9(4). Selected bond angles (deg): N1-Ca1-N2 100.3(1), N1-Ca1-N1A 152.4(2), N1-Ca1-N2A 98.6(1), N2-Ca1-N2A 93.2(1), Ca1-N1-C1 = 155.8(3), Ca1-N1-K1 90.5(1), Ca1-N2-C13 127.0(2), Ca1-N2-K1 90.93(9). The calcium atom is in a distorted tetrahedral environment with N-Ca-N angles between 93.2(1) and 153.4(2)°. Despite the small coordination number of 4, rather large Ca-N bond lengths of 232.9(3) and 239.3(3) pm are observed due to electrostatic repulsion between the amide anions and intramolecular steric strain between the bulky aryl groups of neighboring amido ligands. The flexibility of the Ca-N-C bond angles (155.8(3) and 127.0(2)°) supports the mainly ionic nature of this compound. These tetrakis(anilido)calciates are interconnected

Results and Discussion| 43 by potassium counter cations that bind to the nitrogen atoms (K-N = 287.2(3) and 294.1(3) pm) and saturate their coordination spheres by Lewis acid-EDVHLQWHUDFWLRQVWRWKHʌ-systems of the aryl groups. The high reactivity and the efficiency of this complex to catalyze hydrofunctionalization reaction (hydropentelation such as: hydroamination and hydrophosphanylation) will be shown in a later chapter, can be understood based on: firstly, the pKa values of arylamines (approx. 31 depending on the substitution pattern) are higher than the pka values of most common primary amines such as aniline (30.6), secondary amines like N-methyl-aniline (29.5), diphenylamine (25.0) and than the pKa value of diphenylphosphane (22.9), which enables the deprotonation of these substrates.[173] Secondly, in comparison with complex [1], the small coordination number of calcium and the varying N-Ca-N angles between 93.2(1)° and 153.4(2)° enhance the reactivity in comparison to the calcium complex [1] with angles of around 120°. Due to these findings, the calcium atom is less shielded and the accessibility of calcium by the substrate in complex [2] is facilitated. Furthermore, complex [2] has a remarkable enhancement of the nucleophilicity of the anilide anions, caused by the electrostatic repulsion between the anilide anions and the electron-donating isopropyl groups. Overall complex [2] is a solvent- depleted complex, whereas solvent-free calcium amides like complex [1] dimerize via bridging amido ligands.[168] Additionally, the potassium ions form strong bonds to the aromatic ʌ-systems of the aryl groups, preferring a side-on coordination to the phenyl groups.[174] HASB theory supports the notion that the potassium ion represents a significantly softer cation (Lewis base) than the lighter alkaline metals ions and the doubly charged calcium ions. In heterobimetallic amides of potassium and calcium, the amido anions always bind to the harder and less electropositive divalent calcium ion, forming tetrakis(amido)calciates with tetra-coordinate calcium centers. This work was published in April 2013.[162b]

Results and Discussion| 44

3.2 Reactivity of [K2Ca{N(H)Dipp}4]’[2] in hydropentelation (N, P) reactions.

In calcium-mediated catalytic processes, the calciate [K2Ca{N(H)Dipp}4] (Dipp = C6H3-2,6- i-Pr2) [2] represents an ideal choice because its preparation is straightforward from the metathesis reaction of K{N(H)Dipp} with CaI2, its purification easily succeeds by recrystallization, this complex crystallizes without ligated ether bases and consequently, it can be weighed, handled and stored under an inert atmosphere without aging of the crystalline material due to desolvation and loss of ethereal coligands. In addition, smaller amines easily replace the bulky Dipp-NH2 via transamination reactions in order to release steric pressure.[162b] For evaluation purposes, we maintained both, the diyne system diphenylbutadiyne (due to commercial availability and low costs) and the used catalyst [2] under variation of the reaction conditions and substitution pattern of the primary and secondary arylamines as well as phosphanes.

3.2.1 Addition of primary arylamines

At the beginning of this work, the reactivity of complex [2] has been studied by using this complex to mediate the addition of several primary arylamines (Figure 3.3) across the chosen diyne system.

Figure 3.3: The investigated primary arylamines.

Equimolar amounts of diphenylbutadiyne and substituted primary amines were combined in THF in the presence of 5 mol-% of complex [2] and stirred for three days at room temperature. Afterwards a hydrolytic work-up procedure, an unusual product has been formed, similar to the observation of formation of the naphthalene side product which has

Results and Discussion| 45

been reported by GLOCK et al.[162c] The reaction of one equivalent of 4-tert-butylaniline with two equivalents of diphenylbutadiyne under the above mentioned conditions give product [3] with a yield of 72 % as shown in Scheme 3.3.

Scheme 3.3: The reaction of differently substituted anilines (a, b, c, d) with diphenylbutadiyne, in THF at room temperature.

The formation of product [3] is based on Į-deprotonation steps of 4-tert-butylaniline and formation of a C-C bond leading to 2-tert-butyl-6,7,10,11-tetraphenyl-9H- cyclohepta[c]quinoline.

The 1H NMR spectrum of [3] clearly shows a characteristic ABX coupling pattern for the hydrogen atoms at the seven-membered ring leading to three doublets of doublets (Figure 3.4) with a pseudo-triplet for the CH resonance at į = 6.41 ppm due to very similar vicinal coupling constants. The H atoms of the methylene fragment are magnetically inequivalent 2 with a geminal coupling constant of JH,H = 11.6 Hz and verifying the non-planarity of the cycloheptatriene unit.

Results and Discussion| 46

 )LJXUH +105UHVRQDQFHV 0+]>'@7+)UW RIWKHK\GURJHQDWRPVRIWKH VHYHQPHPEHUHGULQJRIFRPSRXQG>@

In order to propose a reaction mechanism, we repeated the preparation of this compound with partly N-deuterated 4-tert-butylaniline with a deuteration degree of 75 %. This approach yields compound [3], besides its partly deuterated derivatives. The coupling pattern in the 1H NMR spectrum at the CH signal at į = 6.41 ppm enables the assignment and determination of the positions of deuterium atoms (Figure 3.5). The coupling pattern of the endocyclic =CH-CH2- fragment allows the assignment to the moieties CH-CH2, CH-CHD, and CH-CDH. The intensity ratio of the resonances excludes the formation of CH-CD2 units, which would suggest a bimolecular reaction mechanism. This coupling pattern and the resonances of the neighboring methylene group clearly show that there exists no preference for the deuteration at either position and hence no stereo control for the transfer of the ortho- hydrogen atom of the 4-tert-butylphenyl group to the seven-membered ring yielding the methylene group C2B.

Results and Discussion| 47

Figure 3.5: 1H NMR spectrum of the C-H fragments of the seven-membered ring of partly deuterated [3] (top) and with assignment to differently deuterated derivatives (bottom), for the CH group at į = 6.41 ppm.

Results and Discussion| 48

In order to determine the influence of the tert-butyl in the used arylamine (Figure 3.3, a), we investigated several para-substituted arylamines (Figure 3.3, b, c, d). Alteration of the electronic and steric nature of the para-substituent from a electron donating group (tert-butyl (Figure 3.3, a)) to an electron withdrawing group (fluoride (Figure 3.3, b) gave similar products as shown in Scheme 3.3, [4]). 2-Fluoro-6,7,10,11-tetraphenyl-9H-cyclohepta[c]quinolne (product [4]) was obtained in very low yield because the fluoro substituent withdraws electron density through the conjugated ʌ-system of the aromatic ring from the nitrogen atom, reducing the nucleophilicity of the amino functional moiety.[175] Verification of the compositions of [3] and [4] succeeded also by X-ray diffraction experiments at single crystals. Molecular structures and numbering schemes of [3] and [4] are presented in Figure 3.6 ([3] is top and [4] is bottom). The numbering scheme of both compounds is similar and a comparison of selected bond lengths is given in Table 3. These compounds are built from two butadiyne molecules (atoms C1A to C16A and C1B to C16B) and one 4-tert-butylaniline (N1A, C17A to C26A) or 4-fluoroaniline (N1A, F1A, C17A to C22A), respectively. The quinoline fragments show balanced bond lengths which are comparable to those of unsubstituted quinoline.[176] Substituents at the quinoline nucleus of [3] and [4] lead to a slight lengthening between those carbon atoms carrying substituents. The phenyl groups are oriented nearly perpendicular to the ring systems and hence, no interaction between the aromatic phenyl JURXSVDQGWKHʌ-systems of the seven-membered ring can be expected and characteristic C- C single bond values around 149 pm were observed.

Results and Discussion| 49

Figure 3.6: Molecular structures and numbering schemes of [3] (top) and [4] (bottom). The ellipsoids represent a probability of 30 %, H atoms are shown with arbitrary radii. Selected bond lengths are given in Table 3.

Results and Discussion| 50

Table 3: Comparison of selected bond lengths (pm) of 2-(tert-butyl)-6,7,10,11-tetraphenyl- 9H-cyclohepta[c]quinoline [3] and 2-(fluoro)-6,7,10,11-tetraphenyl-9H- cyclohepta[c]quinoline [4].

Bond [3] (R = t-Bu) [4] (R = F) N1A-C1A 131.4(2) 131.4(3) N1A-C17A 137.1(2) 138.0(3) C17A-C18A 140.8(2) 141.5(3) C17A-C22A 141.6(2) 141.5(3) C18A-C19A 137.0(2) 137.5(4) C19A-C20A 141.4(2) 138.7(4) C20A-C21A 138.5(2) 136.4(3) C20A-R 153.2(2) 136.3(3) C21A-C22A 141.6(2) 141.9(3) C1A-C2A 144.4(2) 144.2(3) C1A-C11A 149.1(2) 149.6(3) C2A-C3A 139.5(2) 139.5(3) C2A-C4B 148.6(2) 148.3(3) C3A-C4A 149.2(2) 148.6(3) C3A-C22A 144.6(2) 146.2(3) C4A-C5A 149.4(2) 149.4(3) C4A-C1B 135.6(2) 135.8(3) C1B-C2B 151.8(2) 151.1(3) C1B-C11B 149.0(2) 149.3(3) C2B-C3B 150.3(2) 150.5(3) C3B-C4B 133.8(2) 132.8(3) C4B-C5B 149.0(2) 149.2(3)

To ensure our finding we used similar arylamines with a strongly electron withdrawing group (Trifluoromethyl Figure 3.3, c). But due to the fact that trifluoromethyl group is a stronger electron withdrawing group and bulkier than the fluoro group,[175] no reaction was observed even after applying of harder reaction conditions (refluxing, longer reaction time or higher load of the catalyst). Using unsubstituted arylamine (aniline, Figure 3.3, d) under the previously applied reaction conditions (5 mol-% of the catalyst and 3 days stirring at room temperature) did also not lead to the formation of a similar product. This finding led us to conclude that the used primary arylamine should be substituted with an electron

Results and Discussion| 51 donating group such as methyl, isopropyl or tert-butyl. Therefore, the arylamines e, f and g (Figure 3.3, e, f, g) were investigated. The common features of these three arylamines are that the ortho substitutes are blocked by alkyl groups (methyl, isopropyl or tert-butyl). Consequently, the reaction with diphenylbutadiyne must proceed via a different pathway without ortho-CH activation. The reaction of 2,6-diisopropylaniline with diphenylbutadiyne in a 1:2 ratio for 3 days at room temperature in THF in the presence of a precatalyst load of

5 mol % of K2[Ca{N(H)Dipp}4] according to Scheme 3.4 gives the tetracyclic imine 2,6- diisopropyl-9,11,14,15-tetraphenyl-8-azatetracyclo[8.5.0.01,7.02,13]pentadeca-3,5,7,9,11,14- hexaene [5] with a yield of 82-%.

Scheme 3.4: Calciate-mediated hydroamination of diphenylbutadiyne with 2,6- diisopropylaniline in tetrahydrofuran yielding tetracyclic imine [5]. Verification of the composition of [5] succeeded also by X-ray diffraction experiments of single crystals. Molecular structure and numbering scheme of [5] is presented in Figure 3.7. The labeling of the atoms shows the numbering in accordance with the chemical name for the inner tetracyclic unit, with the nitrogen atom N8 being in position 8. For the numbering of the substituents, the digit of the adjacent ring atom was expanded by an additional digit to distinguish the carbon atoms within a substituent.

Results and Discussion| 52

Figure 3.7: Molecular structure and numbering scheme of [5]. The ellipsoids represent a probability of 40 %, all H atoms are omitted for clarity reasons. Selected bond lengths (pm): C1-C2 156.2(2), C1-C7 150.2(2), C1-C10 151.6(2), C1-C15 154.8(2), C2-C3 150.4(3), C2- C21 155.2(3), C3-C4 134.1(3), C4-C5 145.7(3), C5-C6 135.2(3), C6-C7 144.4(3), C6-C61 152.4(3), C7-N8 131.2(2), N8-C9 141.8(2), C9-C10 136.6(3), C9-C91 147.9(3), C10-C11 145.0(2), C11-C12 135.5(3), C11-C111 149.0(3), C12-C13 151.1(3), C13-C14 153.3(3), C14-C15 134.2(3), C14-C141 147.5(2), C15-C151 147.7(3). The nitrogen atom N8 is bound in a five-membered ring with a C7=N8 double bond and a N8-C9 single bond of 131.2(2) and 141.8(2) pm, respectively. Depending on these values, it is obvious that there is no significant delocalization within the conjugated system. A vast steric strain is introduced at the C1 atom, which is a member of all four cycles. This fact leads to severe deviations from a tetrahedral environment (C-C1-C values vary from

101.2(1) to 120.3(2)°) toward a trigonal- pyramidal environment (according to HOUSER and coworkers, the simple four-FRRUGLQDWH JHRPHWU\ LQGH[ IJ4 allows determination of the geometry of tetra-FRRUGLQDWHDWRPVE\DSSO\LQJWKHHTXDWLRQIJ4 = [36ƒí Į + ȕ)]/141°, with

Įand ȕ being the largest angles. Values of 1 and 0 for IJ4 are obtained for ideal tetrahedral and square-planar environments, respectively, whereas 0.85 and values between 0.07 and 0.64 are symptomatic of trigonal-pyramidal and seesaw geometries, respectively.[177] For C1 in compound [5] this concept JLYHVDYDOXHRIIJ4 = 0.88). In addition, the C1-C bonds are

Results and Discussion| 53 significantly elongated. The adjacent C2 atom shows even stronger deviations from the ideal tetrahedral geometry. The smallest C1-C2-C13 angle shows a value of only 95.7(1)° between three sp3-hybridized carbon atoms and a C2-C13 bond length of 157.5(2) pm. Distortions also widen the angles at the vicinal diphenylethene fragment with C15-C14-C141 and C14-C15-C151 values of 129.9(2) and 130.1(2)°, respectively. In addition, compound [5] contains three chiral carbon atoms at positions C1, C2 and C13, consequently, 8 isomers (2n), but due to the centric triclinic space group (3Ư), the ring strain and the steric effects, the crystalline state consists only two of racemate of isomers. Reaction of a less bulky amine, which is substituted at the ortho-positions by methyl groups, with the same diyne system led to different result. In this case, 2,4,6-trimethylaniline (Figure 3.3, f) and diphenylbutadiyne react at room temperature in THF with a 1:1 ratio in the presence of 5 mol-% of K2[Ca{N(H)-Dipp}4] yielding N-mesityl-7-(E)- ((mesitylimino)(phenyl)methyl)-2,3,6-triphenylcyclohepta-1,3,6-trienylamine [6]. As shown in Scheme 3.5, only those hydrogen atoms are depicted which were transferred from the nitrogen atom of the amine substrate to the carbon atoms of the seven-membered ring.

Scheme 3.5: Calciate-mediated hydroamination of diphenylbutadiyne with 2,4,6- trimethylaniline yielding N-mesityl-7-(E)-((mesitylimino)(phenyl)methyl)-2,3,6- triphenylcyclohepta-1,3,6-trienylamine [6].

Compound [6] represents an asymmetric ȕ-diketimine derivative with an annelated unsaturated seven-membered ring. This structural fragment gives rise to a low field shifted resonance for the N-H···N hydrogen bridge in the 1H NMR spectrum with a chemical shift of į = 12.85 ppm. In Figure 3.8, the 1H NMR spectrum of the methyl region is depicted.

Results and Discussion| 54

This spectrum shows that the 2- and 6- positions are magnetically not equivalent which suggests a hindered rotation of the mesityl groups around the N-C bonds. The non- equivalence of the ortho-methyl groups of each mesityl substituent is also a consequence of the chiral carbon atom of the seven-membered cycloheptatriene ring.

Figure 3.8: The 1H NMR resonances of the methyl substituents of the mesityl groups.

Molecular structure and numbering scheme of compound [6] are shown in Figure 3.9. This compound is built from two butadiyne (atoms C1A to C4A and C1B to C4B) and two 2,4,6-trimethylaniline molecules (N1A, C17A to C25A as well as N1B, C17B to C25B). Compound [6] contains the chiral C4B atom but due to the centric monoclinic space group, the crystalline state consists of a racemate of R- and S-isomers. The structure dominating moiety is the N1A-C1B-C2B-C3B-N1B fragment with significant charge delocalization and a N1B-H···N1A hydrogen bridge (N1A···N1B distance: 265.7(3) pm). The C1A-C2B bond length shows a characteristic single bond value for sp2 hybridized carbon atoms, excluding ʌ-interaction between the ȕ-diketimine uniW DQG WKH UHPDLQLQJ ʌ-bonds of the seven- membered ring. The hydrogen bridge also explains why only the (E)-isomer of the N1A=C1B imine unit is observed.

Results and Discussion| 55

Figure 3.9: Molecular structure and numbering scheme of [6]. The ellipsoids represent a probability of 30 %, selected H atoms are shown with arbitrary radii. Selected bond lengths (pm): N1A-C17A 142.9(3), N1A-C1B 129.5(3), N1B-C17B 143.2(3), N1B-C3B 135.7(3), N1B-H 88(3), C1A-C2A 135.8(3), C1A-C2B 147.2(3), C1A-C11A 149.0(3), C2A-C3A 143.9(3), C3A-C4A 134.7(3), C4A-C5A 148.4(3), C4A-C4B 152.8(3), C1B-C2B 146.9(3), C1B-C11B 150.6(3), C2B-C3B 139.1(3), C3B-C4B 151.6(3), C4B-C5B 153.9(3). In contrast, no reactions were observed between 2,4,6-tri-tert-butylaniline (Figure 3.3, g) and diphenylbutadiyne under the same reaction conditions (5 mol-% of catalyst and 3 days stirring at room temperature), even though this arylamine is substituted with three electron donating groups (tert-butyl) which could be expected to increase the nucleophilicity by LQFUHDVLQJWKHHOHFWURQGHQVLW\WKURXJKWKHFRQMXJDWHGʌ-system of the aromatic ring at the nitrogen atom. The inactivity of arylamine g even while applying harsher reaction conditions, such as refluxing, higher catalyst load or longer time (stirring up to six days), can be referred to the huge steric effect which is caused by the substitution in ortho- and para-positions by tert-butyl. Consequently, arylamine g cannot easily replace the bulky

Dipp-NH2 in the catalyst via transamination reactions in order to release steric pressure. Mechanistically, the aryl Mes* hinders the attack at butadiyne.

In order to study the influence of the reaction temperature, we repeated the previous reactions between the primary arylamines (Figure 3.3) and the diphenylbutadiyne under harsher conditions. The addition of the arylamines (a, b, d, e and f) to diphenylbutadiyne was performed in THF in the presence of 5 mol -% of the catalyst [2] with stirring and refluxing

Results and Discussion| 56

of the reaction mixture for three days. Then additional 5 mol-% of K2[Ca{N(H)Dipp}4] [2] were added and heating was continued for further three days. A standard workup procedure, including hydrolysis with distilled water, extraction with diethyl ether, drying with sodium sulfate, and recrystallization from pentane or toluene at 5 °C yielded colorless crystals of N- aryl-2,5-diphenyl-pyrroles according to Scheme 3.6 ([7]: R = t-Bu, 5¶ +[8]5 )5¶  H; [9]: 5 5¶ 0H [10]5 'LSS5¶ + [11]5 5¶ +  In contrast, application of these new harsh reaction conditions for the arylamines c (4-trifluoromethylaniline) and g did not lead to any increase of their reactivity and no reactions were observed.

6FKHPH  &RPSOH[ >@ PHGLDWHG K\GURDPLQDWLRQ RI GLSKHQ\OEXWDGL\QH ZLWK SULPDU\ DU\ODPLQHVDWKLJKWHPSHUDWXUHV\LHOGLQJ1$U\OGLSKHQ\OS\UUROHV Only those hydrogen atoms that were bound at the nitrogen atom of the amine substrate are depicted. Due to the symmetry of these compounds [7-11], the 1H NMR spectra show singlets for the CH resonances around į = 6.41 ppm. The X-ray diffraction experiments on single crystals succeeded only for compounds [9] and [11]. The molecular structure and numbering scheme of N-mesityl-2,5-diphenylpyrrole [9] and N-phenyl-2,5-diphenylpyrrole [11] are depicted in Figure 3.10 and Figure 3.11, respectively. Due to steric reasons, the N- bound aryl group is oriented nearly perpendicular to the pyrrole ring with an angle of 69.2° between these planes. Expectedly, WKHʌ-system of the pyrrole ring leads to short bonds and charge delocalization to a large extend. Endocyclic C1-C2, C2-C3 and C3-C4 bond lengths differ by less than 3 pm and have an average value of 138.9 pm. The exocyclic C1-C20 and

Results and Discussion| 57

C4-C5 bond lengths with an average distance of 147.2 pm are characteristic for single bonds between sp2-hybridized carbon atoms.

)LJXUH0ROHFXODUVWUXFWXUHDQGQXPEHULQJVFKHPHRI>@7KHHOOLSVRLGVUHSUHVHQWD SUREDELOLW\RI+DWRPVDUHVKRZQZLWKDUELWUDU\UDGLL6HOHFWHGERQGOHQJWKV SP  1&  1&  1&  &&  &&  & &  &&  &&  DQJOHV GHJ &1&  1& &    &&&    &&&    1&&    &1&    &1&    1&&    &&&    1&&   &&&  

1,2,5-Triphenylpyrrole [11] exhibits crystallographic C2 symmetry and shows very similar structural parameters in comparison to compound [9], as shown in Figure 3.11.

Results and Discussion| 58

Figure 3.11: Molecular structure and numbering scheme of 1,2,5-triphenylpyrrole [11]. The ellipsoids represent a probability of 30 %, hydrogen atoms are shown with arbitrary radii. Symmetry-related atoms (-x+2, y, -z+1) are marked with the letter A. Selected bond lengths (pm): N1-C1 138.49(13), C1-C2 138.01(15), C2-C2A 141.7(2), and N1-C9 143.82(18).

Proposed mechanism In all cases, with exception of [3], moderate to good yields were obtained. The precatalyst

K2[Ca{N(H)Dipp}4] [2] reacts with the primary arylamines, and NMR spectroscopic investigations of THF solutions containing K2[Ca{N(H)-Dipp}4] and the 4-fold stoichiometric amount of 2,4,6-trimethylaniline verified the quantitative ligand exchange and formation of 2,6-diisopropylaniline. A 1:2 ratio of [2] and mesitylamine led to heteroleptic calciates of the general formula K2[Ca{N(H)Dipp}4íx{N(H)-Mes}x]. Due to the fact that all aniline derivatives might exhibit comparable pKa values, it can be concluded that the bulkier amide is replaced by the smaller amide in order to minimize intramolecular strain of the calciate anion, mainly provoked by the ortho substituents. The catalytic reaction starts with the addition of a metal-QLWURJHQERQGWRRQH&Ł&WULple bond as shown in Scheme 3.7

Results and Discussion| 59

(nucleophilic attack of an amide at an alkyne) yielding intermediate A. In this scheme, M symbolizes the s-block metal and hence the anionic site.

Scheme 3.7: Proposed mechanism of the complex [2] mediated hydroamination of diphenylbutadiyne with primary arylamines at high temperatures yielding N-aryl-2,5- diphenyl-pyrroles. E/Z-Isomerization is possible via a cumulene isomer A' which can either isomerize to a trans (A) or a cis orientation (A'') of the anionic site and the remaining alkyne moiety. Such cumulene systems have also been suggested during calcium-mediated hydrophosphanylation of diphenylbutadiyne with diphenylphosphane in order to explain isomer mixtures.[51a] After the initial reaction step, intramolecular metalation transfers the N-bound hydrogen to the alkenyl moiety and amide B is formed. During the high temperature route an intramolecular addition to the second alkyne unit occurs and the pyrrole derivative C is formed. The reaction of this intermediate species with another arylamine regenerates the catalyst, and the formation of pyrroles [7-11] is completed. In contrast to this straightforward pathway for the synthesis of pyrroles [7-11], the low temperature route proceeds via an insertion of another diphenylbutadiyne molecule into the newly formed metal-carbon bond (carbometalation step, (Scheme 3.8)), yielding intermediate D. For the sake of clarity, the diphenylbutadiyne units are distinguished by different colors in this scheme. Thereafter an intramolecular

Results and Discussion| 60 metalation forms amide E with a metal-nitrogen bond. Now, three reaction routes seem to be feasible to explain the formation of [3], [4] (via ortho-CH activation), [5] (via cyclization and rearrangement steps) and [6] (via addition of a second arylamine). The closed-shell ionic mechanism involves the formation of the 1,2,4,6-cycloheptatetraene intermediate F with the negative charge at the 5-position (exemplified in the scheme by an M-C bond). Such species exhibit ring strain, nevertheless, unsaturated ring systems of this kind have already been studied in a solid matrix[178] and by quantum chemical investigations, also considering other isomers such as phenylcarbene, bicyclo[3.2.0]hepta-1,3,6-triene, bicyclo[3.2.0]hepta-3,6- diene-2-ylidene, bicyclo[3.2.0]hepta-2,3,6-triene, and bicyclo[4.1.0]heptatriene.[179] Furthermore, a cyclotetramer of such a strained cycloheptatetraene derivative has been characterized by X-ray crystal structure determination.[180] These investigations show that 1,2,4,6-cycloheptatetraene is favored in comparison to a carbene set in a seven-membered ring, and represent 4n ʌ-Möbius aromatic systems.[181] Afterward intramolecular metalation by an arylamine regenerates the catalyst and leads to the formation of G. In this bicyclic intermediate the allene moiety attacks the ortho-CH group leading to compounds [3] and [4]. Absence of o-CH fragments and bulkier N-bond aryl groups favor (in the case of methyl groups) the formation of isomer G', leading to an alternative reaction pattern. Here, the 1,4- addtion of 2,4,6-Trimethylaniline to the cycloheptatetraene ring leads to the formation of compound [6]. In the case of Dipp groups, a cyclization reaction releases the strain of the seven membered ring which is caused by the allene moiety, and annihilates the aromatic character of the Dipp group, resulting intermediate G'', which rearranges and gives compound [5] as shown in Scheme 3.8. An alternative pathway which starts from the bottom of Scheme 3.8, allows the catalyst reformation by an intermolecular reaction with an arylamine and the protonation of E (hence, the formation of metal-free intermediate H).

Thereafter, a BERGMAN cyclization leads to the formation of the diradical species I. This radical can attack either at an o-CH group giving intermediate J, which will yield [3] and [4] by the abstraction of the hydrogen from the amino functionality or in the case of preoccupation of o-positions of the arylamine by methyl group, another amine substrate will be added to intermediate I, leading to compound [6] as shown in Scheme 3.8. In the case of preoccupation of the o-positions of the arylamine by diisopropyl groups, the diradical species I will rearrange to the tricyclic imine G'', accompanied by a hydrogen abstraction from the

Results and Discussion| 61 amino functionality. This hydrogen transfer from the amino unit to the carbon atom is accompanied by C-C bond formation, leading to a breakup of the aromaticity of the former Dipp group as shown in Scheme 3.8.

Results and Discussion| 63

,QVXPPDU\K\GURDPLQDWLRQRISULPDU\DU\ODPLQHVRFFXUVVXFFHVVIXOO\XQGHUWZRSDWKZD\V GHSHQGLQJRQWKHUHDFWLRQFRQGLWLRQV L NLQHWLFFRQWURO PRORIWKHFDWDO\VWDQGGD\V VWLUULQJDWURRPWHPSHUDWXUH OHDGVWRUDWKHUFRPSOH[UHDFWLRQSDWKZD\VGHSHQGLQJRQWKH RUWKRVXEVWLWXHQWVRIWKHDU\ODPLQHVDQGWKHIRUPDWLRQRIXQVDWXUDWHGVHYHQPHPEHUHGULQJV UHSUHVHQWVDNH\IHDWXUHRU LL GXULQJWKHUPRG\QDPLFFRQWURO îPRORIWKHFDWDO\VW DQGîGD\VVWLUULQJDQGUHIOX[LQJWKHK\GURDPLQDWLRQRIGLSKHQ\OEXWDGL\QHZLWKSULPDU\

DU\ODPLQHVHPSOR\LQJ.>&D^1 + 'LSS`@\LHOGV1DU\OGLSKHQ\OS\UUROHVDVVKRZQLQ WKH RYHUYLHZ VFKHPH 6FKHPH   RI WKH DGGLWLRQ RI SULPDU\ DU\ODPLQHV )LJXUH   DFURVVGLSKHQ\OEXWDGL\QH

Results and Discussion| 64

Scheme 3.9: Addition of primary arylamines across diphenylbutadiyne under two different reaction conditions ((i) and (ii)).

This work was published in 2015.[182]

Results and Discussion| 65

3.2.2 Addition of secondary arylamines

In order to shed light on the first reaction step we blocked one of the primary arylamine hydrogen atoms by using the N-methylatedanilines. N-methyl-aniline, N-methyl-para- tolylamine, N-methyl-4-fluoro-aniline and N-methyl-4-(trifluoromethyl)aniline (Figure 3.12, h-k).

Figure 3.12: The investigated secondary arylamines.

GLOCK el at. showed that the hydroamination of diphenylbutadiyne with diphenylamine required a significantly reactive catalyst system such as dipotassium calciate [K2Ca(NPh2)4]. During these calcium-mediated hydroamination reactions only singly hydroaminated butadiynes were isolated whereas the second CŁC triple bond remained intact.[162c] In contrast to theses initial investigations, the use of complex [2] to catalyze the hydroamination of diphenylbutadiyne with various secondary arylamines (Figure 3.12, h-j), gave surprising results, where the second CŁC triple bond of the butadiyne system was hydroaminated as well and doubly hydroaminated butadiynes were isolated.

Singly hydroaminated diphenylbutadiyne

In these studies, we used the same catalyst (complex [2]) as well as the same butadiyne system (diphenylbutadiyne) and diverse secondary arylamines. The use of secondary arylamines guarantees that the rather complex cyclization reactions are suppressed. N- Methyl-arylamines were reacted with diphenylbutadiyne in the presence of catalytic

Results and Discussion| 66

amounts of [K2Ca{N(H)Dipp}4]([2]). In a standard procedure, diphenylbutadiyne was dissolved in THF. At room temperature, an equimolar amount of N-methyl-arylamine

HN(Me)C6H4-4-R (R = H, Me, F, CF3) and 5 mol-% of the catalyst were added. This solution was stirred for several hours at room temperature. Repeated NMR measurements showed that in all cases, with the exception of arylamine k (Figure 3.12, k), the conversion of the secondary arylamine and the formation of singly hydroaminated diphenylbutadiyne was successful (R = H [12], Me [13], F [14]) and mixtures of E- and Z-isomers according to Scheme 3.10. After quantitative conversion the reaction mixture was hydrolyzed with distilled water, the aqueous solution was extracted with diethyl ether. The ether fractions were combined, dried with sodium sulfate, then the ether was removed yielding the tertiary amines 1-(N-methyl-anilino)-1,4-diphenylbut-1-ene-3-yne with E/Z ratios of approximately 1 : 0.6 [12], 1 : 1 [13] and 1 : 0.9 [14].

Scheme 3.10: Single hydroaminated diphenylbutadiyne.

Recrystallization from a solvent mixture of dichloromethane and pentane gave pure compounds. However, the different isomers exhibited rather similar solubility properties hampering a fractional crystallization under these conditions. Verification of the composition of [12], [13] and [14] was successful by X-ray diffraction experiments on single crystals. Molecular structures and numbering schemes of compounds [12], [13] and [14] are presented in Figure 3.13, Figure 3.14 and Figure 3.15, respectively.

Results and Discussion| 67

Figure 3.13: Molecular structure and numbering scheme of E-[12].The ellipsoids represent a probability of 30 %, H atoms are drawn with arbitrary radii. Selected bond lengths and angles are listed in Table 4.

Figure 3.14: Molecular structure and numbering scheme of E-[13].The ellipsoids represent a probability of 30 %, H atoms are drawn with arbitrary radii. Selected bond lengths and angles are listed in Table 4.

Results and Discussion| 68

Figure 3.15: Molecular structure and numbering scheme of E-[14]. The ellipsoids represent a probability of 30 %, H atoms are drawn with arbitrary radii. Selected structural parameters are listed in Table 4.

The molecular structure and numbering scheme of E-(1,4-diphenylbut-1-ene-3-yne-1-yl)-(4- fluorophenyl)-methylamine (E-[14]) is depicted in Figure 3.15. The essential structural parameters of E-[12], E-[13], and E-[14] are very similar and summarized in Table 4. The nitrogen atom N1 is in a nearly planar environment allowing conjugation of the lone pair with the but-1-ene- 3-yne unit. The N1-C17 and N1-C18 bond lengths represent characteristic N-C values to sp3 and sp2 hybridized carbon atoms, respectively. The shorter N1-C1 bond lengths hint toward a slight conjugatiRQZLWKWKHDONHQHPRLHWLHV7KHʌ-system of the alkene fragments do not interact with the adjacent phenyl group. The C1=C2 double bonds (135.3 to 135.8 pm) are only slightly elongated compared to the expected value of a double bond between sp2 hybridized carbon atoms (134 pm).[183] The C3ŁC4 triple bonds reflect the characteristic values of an isolated triple bond.

Results and Discussion| 69

Table 4: Selected structural parameters (bond lengths [pm] and angles [deg.]) of the E- isomers E-[12], E-[13], and E-[14].

E-[12] E-[13] E-[14] N1-C17 146.78(16) 146.78(18) 146.76(13) N1-C18 143.17(16) 143.10(17) 143.19(13) N1-C1 139.99(15) 139.94(17) 139.97(13) C1-C11 148.74(17) 149.09(18) 149.18(14) C1-C2 135.33(17) 135.53(19) 135.77(15) C2-C3 142.34(17) 142.29(19) 142.37(15) C3-C4 120.27(18) 120.31(19) 120.40(15) C4-C5 143.39(17) 143.38(19) 143.61(14) C17-N1-C18 115.11(10) 115.06(11) 114.81(8) C1-N1-C17 117.79(10) 117.88(11) 117.92(9) C1-N1-C18 117.95(10) 119.37(11) 118.38(8) N1-C1-C2 122.06(11) 121.07(12) 121.68(9) N1-C1-C11 115.49(10) 115.49(11) 115.75(9) C2-C1-C11 122.21(11) 123.22(12) 122.38(9) C1-C2-C3 125.01(12) 126.78(13) 125.86(10) C2-C3-C4 176.09(13) 173.87(14) 175.45(11) C3-C4-C5 176.23(13) 177.59(14) 177.34(11)

Selected NMR data are summarized in Table 5. The numbering scheme for the carbon atoms is identical to the numbering of the X-ray structures discussed above. For the assignment, single crystals of the E-isomers were dissolved in an appropriate solvent and 2D-NMR experiments (H,H-COSY, HMBC and HSQC spectra) allowed an unambiguous assignment of these resonances, an assignment to specific carbon atoms was not possible. Thereafter, a mixture of both isomers allowed to assign also the resonances of the Z-isomers. The hydrogen atoms at the C2 atoms clearly allow to distinguish between the E- and Z-isomer because the resonances of the E-isomers are shifted toward a lower field by approx.'G = 0.5 ppm. A comparable effect, albeit smaller, is also observed for the N-bound methyl groups. In the 13C{1H} NMR spectra only small differences of the chemical shifts of the isomers can be found.

Results and Discussion| 70

Table 5: Selected NMR data of the singly hydroaminated diphenylbutadiyne. The numbering scheme is identical with the molecular structures and can be seen in Figure 3.13, Figure 3.14 and Figure 3.15

E-[12] E-[12] Z-[12] E-[13] Z-[13] E-[14] Z-[14]

Solvent DMSO [D8]THF [D8]THF [D8]THF [D8]THF CD2Cl2 CD2Cl2 1H C2-H 5.96 5.83 5.28 5.69 5.17 5.75 5.21 C17-H 3.34 3.40 3.25 3.42 3.26 3.40 3.23

13C{1H} C1 155.1 155.9 158.2 156.2 158.2 157.9 160.5 C2 99.9 100.3 90.6 88.8 87.5 88.3 88.9 C3 97.4 98.4 90.8 a 90.6 a 90.9 a 99.1 97.9 C4 88.3 88.6 91.1 a 91.1 a 90.1 a 90.5 90.4 C11 137.6 139.3 137.7 139.6 137.2 137.1 138.8 C17 39.4 39.5 41.5 40.0 42.2 41.6 39.7 C18 147.0 148.3 149.2 146.7 146.1 144.6 145.1 a) Assignment uncertain.

In contrast, no reactions were observed between N-methyl-4-(trifluoromethyl)aniline (Figure 3.12, k) and diphenylbutadiyne under the same reaction conditions (5 mol-% of the catalyst and 3 days stirring at room temperature). This secondary arylamine k is substituted with an electron withdrawing group (-CF3) in para-position, which reduces the nucleophilicity by decreasing WKHHOHFWURQGHQVLW\WKURXJKWKHFRQMXJDWHGʌ-system of the aromatic ring from the nitrogen atom. Hence, no reactions could be occurred under the same conditions.

The reaction mechanism of the addition of the secondary arylamines across diphenylbutadiyne is less complicated than the addition of the primary arylamines, because the catalytic cyclization reactions are suppressed. In order to release steric pressure, which the precatalyst [K2Ca{N(H)Dipp}4] ([2]) possess, at least one diisopropylanilide anion is exchanged by an N-methyl-arylamide through a transamination reaction, forming the catalytically active species yielding LnCa-NRR' as shown in Scheme 3.11. L represents a Lewis base such as a solvent molecule (thf), an amine or an amide anion. The Ca-N bond DGGVWRD&Ł&WULSOHERQGOHDGLQJWRLQWHUPHGLDWHA. The newly formed and highly reactive

Results and Discussion| 71

Ca-C moiety metalates an amine finally yielding the E-isomer and regenerating the catalyst. Even though the E-isomers represent the major product, significant amounts of the Z-isomers are observed. A 1,3-shift of the negative charge leads to the formation of cumulene B (which might also exist as a solvent-separated ion pair). From this isomer, the back reaction reforms isomer A, whereas also the other isomer C can be obtained. Metalation of the amine by C yields the Z-isomer (Scheme 3.11).

Scheme 3.11: Proposed catalytic cycle for the calcium-mediated hydroamination of diphenylbutadiyne (Ph = phenyl; R, R' = methyl aryl). Due to the fact that the exact composition of the catalytic species is unknown, the calcium catalyst is shown as [LnCaNRR'] with L representing any Lewis base such as thf (solvent), amines and amides such as the anions NRR'- and N(H)Dipp-.

Results and Discussion| 72

Doubly hydroaminated diphenylbutadiyne

The reaction of diphenylbutadiyne with two equivalents of N-methyl-aniline and N-methyl- 4-fluoroaniline (Figure 3.12,h, j) after three days yielded an E/Z-isomeric mixture of 1,4- di(N-methyl-anilino)-1,4-diphenylbuta-1,3-diene [15] and 1,4-Diphenyl-1,4-bis(N-methyl- 4-fluoroanilino)buta-1,3-diene [16], respectively as shown in Scheme 3.12.

Scheme 3.12: Synthesis of doubly hydroaminated diphenylbutadiyne.

The conversion was monitored by NMR spectroscopic measurements as depicted in Figure 3.16. These NMR studies showed that the formation of the E-isomer is favored, but again cis- and trans-addition was observed for the second hydroamination step, yielding E,Z- and E,E-1,4-di(N-methyl-anilino)-1,4-diphenylbuta-1,3-diene ([15]) as the major components. The E,E- and Z,Z-isomers are formed with a ratio of 3:1. This is in agreement with the formation of the singly hydroaminated compounds E-[12] and Z-[12] where the E-isomer also represents the favored product. The progress of the second hydroamination step can be elucidated from the resonances of the alkene protons in the region between į = 5.3 and 7.0 ppm. The spectra were recorded after 1 h, 5 h, 21 h, 29 h, 59 h, and 72 h (Figure 3.16, from bottom to top) after mixing of the substrates. In the bottom spectrum E-[12] (į = 5.82 ppm) and Z-[12] (į = 5.28 ppm) are the major components; after 72 h, these compounds together with the doubly hydroaminated diphenylbutadiynes E,E-[15] (į = 6.59 ppm), E,Z-[15] (į =

Results and Discussion| 73

5.93 and 6.7 ppm), and Z,Z-[15] (į = 6.26 ppm) are observed, respectively. A complete conversion was not achieved under these reaction conditions. A final NMR experiment approximately after one-month reaction time still contained singly hydroaminated [12].

Figure 3.16: NMR spectroscopic monitoring of the second hydroamination of an E/Z- mixture of [12]. The time-dependent conversion of the singly hydroaminated diphenylbutadiyne [12] to the doubly hydroaminated derivatives [15] is depicted in Figure 3.17. The s-block metal- mediated hydroamination of the second CŁC triple bond of diphenylbutadiyne is significantly slower than the first hydroamination process, allowing the isolation of the pure mono-hydroamination product [12]. However, the mono-hydroaminated product was still present after several days or even weeks. Thus, the reaction solution showed a mixture of 10 % of Z-[12] and 20 % of E-[12] as well as 30-% of E,E-[15], 30 % of E,Z-[15] and 10 % of Z,Z-[15] after 72 hours.

Results and Discussion| 74

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The bulkier N-methyl-p-toluidine (Figure 3.12, i) reacted only once, regardless of the applied stoichiometry giving exclusively the singly hydroaminated product [13] with the same ratio of E- and Z-isomers. In contrast to this inhibition by a para-methyl substituent, the hydroamination of diphenylbutadiyne with N-methyl-para-fluoroaniline (Figure 3.12, j) showed that the second hydroamination step also occurred readily leading to E/Z-mixtures of 1,4-di(N-methyl-para-fluoroanilino)-1,4-diphenylbuta-1,3-diene [16]. The reaction of 1- (N-methyl-anilino)-1,4-diphenylbut-1-ene-3-yne [12] with N-methyl-para-fluoroaniline led to the formation of the asymmetric 1,4-hydroaminated butadiene derivative [17]. Due to the lack of formation of symmetric [15] and [16], an equilibrium with amination-deamination pathways can be excluded. In contrast to these findings, N-methyl-toluidine again showed QRWHQGHQF\WRUHDFWZLWKWKHVHFRQG&Ł&WULSOHERQGRI[12] under these reaction conditions.

Results and Discussion| 75

The centrosymmetric molecular structures of the doubly hydroaminated isomers E,E-[15] and Z,Z-[16] are displayed in Figure 3.18 and Figure 3.19, respectively.

Figure 3.18: Molecular structure and numbering scheme of centrosymmetric E,E-[15]. Symmetry-related atoms are marked with the letter "A". The ellipsoids represent a probability of 30 %, H atoms are shown with arbitrary radii. Selected structural parameters are listed in Table 6.

Results and Discussion| 76

Figure 3.19: Molecular structure and numbering scheme of centrosymmetric Z,Z-[16]. Symmetry-related atoms are marked with the letter "A". The ellipsoids represent a probability of 30 %, H atoms are drawn with arbitrary radii. Selected bond lengths and angles are summarized in Table 6. The asymmetric derivative [17] crystallized as a Z,Z-isomer in the centrosymmetric monoclinic space group P21/c with the center of symmetry on the butadiene unit leading to

Results and Discussion| 77

1:1 disordering of the 4-fluorophenyl and the N-bound unsubstituted phenyl groups. In Figure 3.20, the C-F and C-H bonds to the disordered atoms with occupancy factors of 50 % are shown as broken lines; only one orientation of this molecule is depicted. Due to the fact that the influence of the para-positioned substituents on the structure of the central moieties is negligible in the singly hydroaminated derivatives ([12], [13] or [14]), their structural parameters are reliable. Selected structural data are summarized in Table 6.

)LJXUH  0ROHFXODU VWUXFWXUH DQG QXPEHULQJ VFKHPH RI ==>@ 6\PPHWU\UHODWHG DWRPVDUHPDUNHGZLWKWKHOHWWHU$'XHWRWKHFHQWURV\PPHWU\WKHIOXRULQHDQGK\GURJHQ DWRPVDW& WKHUHVSHFWLYHERQGVDUHGHSLFWHGDVEURNHQOLQHV LVGLVRUGHUHGZLWKDUDWLR RQO\RQHRULHQWDWLRQLVGHSLFWHGLQWKLVILJXUH7KHHOOLSVRLGVUHSUHVHQWDSUREDELOLW\RI +DWRPVDUHVKRZQZLWKDUELWUDU\UDGLL

Results and Discussion| 78

The central butadiene units resemble characteristic bond lengths of C-C single and C=C double bonds without significant charge delocalization. In agreement with this interpretation, the C1-C10 bond lengths to the phenyl groups resemble characteristic single bond values between sp2 hybridized carbon atoms.[183] Due to the crystallographic inversion symmetry, the buta-1,3-diene units are strictly planar. According to the VSEPR concept multiple bonds are more demanding than single bonds and therefore, they require more space leading to decreased N1-C1-C11 bond angles. Table 6: Selected structural parameters (bond lengths [pm] and angles [°]) of doubly hydroaminated diphenylbutadiyne.

E,E-[15] Z,Z-[16] Z,Z-[17] N1-C4 141.9(3) 139.5(3) 139.2(3) N1-C3 146.2(3) 146.0(3) 145.7(3) N1-C1 141.4(3) 143.1(3) 142.9(2) C1-C10 148.3(4) 147.7(4) 148.1(3) C1-C2 136.0(4) 135.1(4) 135.1(3) C2-C2A 143.8(5) 143.8(5) 144.3(4) C3-N1-C4 116.9(2) 119.0(2) 119.8(2) C1-N1-C3 117.6(2) 117.0(2) 118.6(2) C1-N1-C4 120.8(2) 121.5(2) 121.5(2) C2-C1-C10 123.8(2) 122.0(2) 122.4(2) N1-C1-C10 115.1(2) 117.2(2) 117.5(2) N1-C1-C2 121.1(2) 120.8(2) 119.8(2) C1-C2-C2a 126.6(3) 125.5(3) 125.0(2)

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Results and Discussion| 79

,Q VXPPDU\ WKH SUHFDWDO\VW >.&D^1 + 'LSS`@ >@  ZDV HPSOR\HG WR VWXG\ WKH K\GURDPLQDWLRQ RI GLSKHQ\OEXWDGL\QH ZLWK VHFRQGDU\ 1PHWK\ODU\ODPLQHV LQ WHWUDK\GURIXUDQDWURRPWHPSHUDWXUH$IWHUDSSUR[LPDWHO\KDQHDUO\FRPSOHWHFRQYHUVLRQ ZLWKDFDWDO\VWORDGLQJRIPROOHGWRVLQJO\K\GURDPLQDWHGEXWDGL\QH FRQGLWLRQV L LQ 6FKHPH 7KHVHFRQGK\GURDPLQDWLRQVWHSRIWKHRWKHU&Ł&WULSOHERQGUHTXLUHVPXFK ORQJHUWLPHDWVLPLODUUHDFWLRQFRQGLWLRQV FRQGLWLRQV LL LQ6FKHPH $IWHUWKUHHGD\V PL[WXUHV RI VLQJO\ DQG GRXEO\ K\GURDPLQDWHG GLSKHQ\OEXWDGL\QH ZHUH REWDLQHG LI 1 PHWK\ODQLOLQH DQG 1PHWK\OIOXRURDQLOLQH ZHUH HPSOR\HG ,Q FRQWUDVW QR VLJQLILFDQW DPRXQWVRIGRXEO\K\GURDPLQDWHGGLSKHQ\OEXWDGL\QHZDVREVHUYHGIRUWKHK\GURDPLQDWLRQ ZLWK1PHWK\OWRO\ODPLQH

Results and Discussion| 80

6FKHPH  $GGLWLRQ RI VHFRQGDU\ DU\ODPLQHV DFURVV GLSKHQ\OEXWDGL\QH XQGHU WZR GLIIHUHQWUHDFWLRQFRQGLWLRQV L DQG LL 

This work was published in 2016.[184]

Results and Discussion| 81

3.2.3 Addition of diphenylphosphane

In 2012 GLOCK et al. synthesized the singly hydroaminated E- and Z-isomers of 1- diphenylamino-1,4-diphenylbut-1-ene-3-yne via reacting diphenylbutadiyne with diphenylamine in the presence of [K2Ca(NPh2)4] as catalyst in boiling THF for 6 hours. In this reaction the high temperature was required for enhancement of the catalyst reactivity and, hence, the conversion of the products.[162c] Afterwards these products were hydrophosphanylated with diphenylphosphane in tetrahydrofuran in the presence of 5 mol-

% of [(thf)4Ca(PPh2)2] quantitatively yielding 1-diphenylamino-1,4-diphenyl-4- diphenylphosphanylbuta-1,3-diene by WESTERHAUSEN et al.[185] The E/Z-isomerism at the amino functionality is maintained, whereas only the E-isomeric hydrophosphanylation was observed according to Scheme 3.14.

Scheme 3.14: Two-step synthesis of 1-(diphenylamino)-1,4-diphenyl-4- (diphenylphosphanyl)buta-1,3-diene using different calcium-based catalysts for the hydropentelation reactions. These findings suggest that the synthesis of substituted 1-amino-4-phosphanylbuta-1,3- dienes requires the hydroamination as the initial step and the hydrophosphanylation as a subsequent reaction.

Results and Discussion| 82

In order to study the reactivity of the calciate precatalyst [2] in the hydrophosphanylation reactions and hence the elimination of the necessity to change the calcium-based catalyst from the K2Ca(NHRR`)4 for the hydroamination to [(thf)4Ca(PPh2)2] for the subsequent hydrophosphanylation step, we repeated this catalytic hydrophosphanylation of 1-(diphenylamino)-1,4-diphenylbut-1-ene-3-yne by using catalytic amounts of

K2[Ca{N(H)Dipp}4] ([2]). After complete conversion, the solvent was removed and the residue dissolved in methanol to inactivate the calcium catalyst. After removal of methanol, the residue was dissolved in methylene chloride and filtered to remove the calcium- containing compounds. Thereafter, recrystallization from methylene chloride/pentane again provided yellow crystals of E/E-[18] and Z/E-[18] as shown in Scheme 3.15.

Scheme 3.15: Hydroamination and hydrophosphanylation of diphenylbutadiyne provided by K2[Ca{N(H)Dipp}4].

7KLVUHVXOWVXJJHVWVWKDWWKHWZRGLIIHUHQWK\GURHOHPHQWDWLRQUHDFWLRQVFRXOGEHSHUIRUPHG ZLWKRXWDFKDQJHRIWKHFDWDO\VWV\VWHPDQGZLWKRXWWKHQHHGWRLVRODWHWKHK\GURDPLQDWLRQ SURGXFWSULRUWRWKHK\GURSKRVSKDQ\ODWLRQUHDFWLRQ The structural elucidation of the compositions of E,E-[18] and E,Z-[18] succeeded by X-ray diffraction experiments at single crystals. Molecular structures and numbering schemes of E,E-[18] and Z,E-[18] are presented in Figure 3.21 and Figure 3.22, respectively. Selected structural parameters are summarized in Table 7.

Results and Discussion| 83

Figure 3.21: Molecular structure and numbering scheme of (E,E)-1-diphenylphosphanyl- 1,4-diphenyl-4-(diphenylamino)buta-1,3-diene (E,E-[18]). The ellipsoids represent a probability of 30 %, H atoms are shown with arbitrary radii.

Results and Discussion| 84

Figure 3.22: Molecular structure and numbering scheme of (E,Z)-1-diphenylphosphanyl- 1,4-diphenyl-4-(diphenylamino)buta-1,3-diene (E,Z-[18]). The ellipsoids represent a probability of 30 %, H atoms are shown with arbitrary radii. In order to ensure our finding, that the hydrophosphanylation occurs regio- and stereoselective to the E-isomeric hydrophosphanylation products, we investigated our singly hydroaminated products 1-(N-methyl-anilino)-1,4-diphenylbut-1-ene-3-yne ([12]) and 1-(N- methyl-tolylamino)-1,4-diphenylbut-1-ene-3-yne ([13]) in hydrophosphanylation reactions. Under the same conditions which have been employed to synthesize 1- (diphenylphosphanyl)-1,4-diphenyl-4-(diphenylamino)buta-1,3-diene [18], diphenylphosphane was added to this reaction mixture, yielding the appropriate hydrofunctionalization products 1-(diphenylphosphanyl)-1,4-diphenyl-4-(N-methyl- anilino)buta-1,3-diene [19] and 1-(diphenylphosphanyl)-1,4-diphenyl-4-(N-methyl- tolylamino)buta-1,3-diene [20] according to Scheme 3.16. Again, the initial hydroamination reaction gave an E/Z-isomeric mixture, whereas the hydrophosphanylation occurred regio- and stereoselective to the E-isomeric hydrophosphanylation products.

Results and Discussion| 85

Scheme 3.16: Calcium-mediated synthesis of 1-(diphenylphosphanyl)-1,4-diphenyl-4-(N- methylanilino)buta-1,3-dienes (R= H [19], Me [20]).

Isolation of the intermediate hydroamination products 1-amino-1,4-diphenylbut-1-ene-3- yne proved to be advantageous in order to prevent impurities of bis-hydroaminated compounds. Unreacted butadiyne also has to be removed prior to the hydrophosphanylation procedures, otherwise the product contained bis-hydrophosphanylated derivatives as well. These side-products hamper the isolation of analytically pure 1-(diphenylphosphanyl)-1,4- diphenyl-4-(amino)buta-1,3-diene and, hence, lower the yields. Therefore, the preferred method involves an initial hydroamination reaction, catalyzed by K2[Ca{N(H)Dipp}4] ([2]), followed by isolation and purification of 1-amino-1,4-diphenylbut-1-ene-3-yne. Thereafter, the hydrophosphanylation of this amine led to E,Z- and E,E-isomeric 1- (diphenylphosphanyl)-1,4-diphenyl-4-(amino)buta-1,3-dienes. This finding is most probably the consequence of steric strain but electronic effects may also play a minor role. Verification of the compositions [19] and [20] succeeded also by X-ray diffraction experiments at single crystals. Molecular structures and numbering schemes of E,Z-[19], E,E-[20] are presented in Figure 3.23 and Figure 3.24, respectively. Selected structural parameters are summarized and compared in Table 7.

Results and Discussion| 86

)LJXUHMolecular structure and numbering scheme of (E,Z)-1-( diphenylphosphanyl)- 1,4-diphenyl-4-(N-methyl-anilino)buta-1,3-diene (E,Z-[19]). The ellipsoids represent a probability of 30 %, H atoms are drawn with arbitrary radii.

Results and Discussion| 87

Figure 3.24: : Molecular structure and numbering scheme of (E,Z)1-(diphenylphosphanyl)- 1,4-diphenyl-4-(N-methyl-tolylamino)buta-1,3-diene (E,Z-[20]). The ellipsoids represent a probability of 30 %, H atoms are drawn with arbitrary radii.

The molecular structures of (E,E)-1-( diphenylphosphanyl)-1,4-diphenyl-4- (diphenylamino)buta-1,3-diene (E,E-[18]), (E,Z)-1-( diphenylphosphanyl)-1,4-diphenyl-4- (diphenylamino)buta-1,3-diene (E,Z-[18]), (Z,E)-1-(diphenylphosphanyl)-1,4-diphenyl-4- (N-methyl-anilino)buta-1,3-diene (Z,E-[19]) and (E,Z)1-(diphenylphosphanyl)-1,4- diphenyl-4-(N-methyl-tolylamino)buta-1,3-diene (E,Z-[20]) show regardless of the isomerism high similarities. Selected structural parameters are compared in Table 7. The butadiene fragment shows no delocalization, typical C=C and C-C bond lengths of approximately 135 and 145 pm, respectively, are observed. Due to steric reasons, the planar amino group is twisted toward the planar butadiene plane and therefore, the electron pair with 1FDQQRWLQWHUDFWZLWKWKHʌ-system of the butadiene moiety. In contrast to the amino group, the phosphorus atom is in a trigonal pyramidal environment with C-P-C bond angles of about 102°. Steric strain between the substituents in 1- and 4-position leads to a distortion

Results and Discussion| 88 of the C-C-C bond angles of the butadiene fragment. The C1-C2-C3 and C2-C3-C4 bond angles of E,E-[18] are both significantly widened whereas for all E,Z isomers the enhancement of these bond angles are smaller. This fact verifies a smaller intramolecular steric strain for the E,Z isomers than for the E,E derivatives. Lack of interaction between the phosphanyl- end groups and the butadiene units leads to very similar P-C bonds of approximately 183 pm to the phenyl and butadiene moieties in all these compounds representing a characteristic P-C single bond value.

Results and Discussion| 89

Table 7: Selected structural parameters of (E,E)-1-(diphenylphosphanyl)-1,4-diphenyl-4- (diphenylamino)buta-1,3-diene (E,E-[18]), (E,Z)-1-(diphenylphosphanyl)-1,4-diphenyl-4- (diphenylamino)buta-1,3-diene (E,Z-[18]), (Z,E)-1-(diphenylphosphanyl)-1,4-diphenyl-4- (N-methyl-anilino)buta-1,3-diene (Z,E-[19]) and (E,Z)1-(diphenylphosphanyl)-1,4- diphenyl-4-(N-methyl-tolylamino)buta-1,3-diene (E,Z-[20]).

E,E-18 E,Z-18 E,Z-19 E,Z-[20]

P1-C1 182.9(2) 183.6(2) 183.5(3) 182.7(4) C1-C2 135.5(3) 134.6(2) 135.2(4) 134.0(6) C2-C3 144.6(3) 145.0(2) 144.7(4) 144.8(6) C3-C4 134.9(3) 135.3(2) 135.1(4) 135.6(6) N1-C4 143.3(3) 142.3(2) 142.0(4) 141.4(5) P1-C5 182.0(3) 183.6(2) 183.4(3) 182.9(5) P1-C11 182.3(3) 182.9(2) 183.8(2) 182.9(4) C1-C17 148.4(3) 148.4(2) 149.3(4) 149.6(6) C4-C23 148.7(4) 147.6(2) 148.7(4) 148.0(6) N1-C29 143.5(3) 141.5(2) 139.5(4) 141.2(6) N1-C35 142.9(3) 142.6(2) 146.1(4) 145.0(6) C1-P1-C5 102.1(1) 102.10(8) 102.2(1) 103.6(2) C1-P1-C11 102.7(1) 102.11(8) 103.8(1) 102.7(2) C5-P1-C11 103.9(1) 102.44(8) 102.5(1) 103.3(2) P1-C1-C2 122.1(2) 121.7(1) 121.8(2) 123.0(3) C1-C2-C3 125.2(2) 127.7(2) 126.9(3) 126.5(4) C2-C3-C4 127.1(2) 122.3(2) 122.1(3) 124.8(4) C3-C4-N1 118.8(2) 118.8(2) 120.7(2) 120.0(4) C4-N1-C29 117.3(2) 120.1(1) 120.4(2) 120.8(3) C4-N1-C35 117.7(2) 119.5(1) 119.5(3) 119.0(4) C29-N1-C35 118.8(2) 120.1(1) 119.9(3) 118.8(4)

Results and Discussion| 90

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Results and Discussion| 91

7DEOHSelected NMR data of the E,E and E,Z isomers of 1-(diphenylphosphanyl)-1,4- diphenyl-4-(diphenylamino)buta-1,3-diene ([18]), 1-(diphenylphosphanyl)-1,4-diphenyl-4- (N-methyl-anilino)buta-1,3-diene ([19]), and 1-(diphenylphosphanyl)-1,4-diphenyl-4-(N- methyl-tolylamino)-buta-1,3-diene ([20]).

E,E-[18] Z,E-[18] E,E-[19] Z,E-[19] E,E-[20] Z,E-[20]

1H NMR

į &-H) 6.39 6.29 6.27 6.01 6.31 6.03 į &-H) 6.62 6.45 6.49 6.51 6.49 6.42 3J(H,H) 8.3 5.3 8.2 5.9 8.5 6.0 3J(H,P) 12.1 10.7 11.6 10.9 11.5 10.9

į 1-CH3) - - 3.04 2.82 2.96 2.81

13C{1H} NMR

į C1) 140.6 140.4 141.8 141.1 140.3 142.4 1J(C,P) 23.1 23.1 19.8 22.1 22.2 22.7

į C2) 136.4 135.0 136.2 136.2 136.1 135.5 2J(C,P) 11.7 12.1 12.3 12.3 10.8 12.4

į C3) 146.7 145.7 147.5 147.5 146.6 147.0 3J(C,P) 2.5 2.1 2.1 2.1 2.8 2.2

į C4) 147.5 147.1 151.6 149.5 152.0 156.0 4J(C,P) ------

į 1-CH3) - - 40.9 38.1 38 37.5

31P{1H} NMR

į P1) 4.45 2.54 4.70 2.28 4.96 2.35

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Results and Discussion| 92

DEOH WR LVRODWH DQG FU\VWDOOL]H WKH (= LVRPHUV RI DOO UHSRUWHG GHULYDWLYHV ZKHUHDV WKH SDUDPHWHUVRIWKH((LVRPHULFFRPSRXQGVKDGWREHHOXFLGDWHGIURPLVRPHULFPL[WXUHV

Proposed Mechanism

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Results and Discussion| 93

Scheme 3.17: The proposed catalytic cycles shown as a two-step process of subsequent hydroamination and hydrophosphanylation reactions. The bottom part shows the hydroamination and offers an explanation for the Z/E-isomerism. In the second hydrophosphanylation catalysis, the H-P bond adds to the second alkyne unit. The thus formed Ca-P bond adds to the remaining alkyne moiety followed by a metalation reaction.

Results and Discussion| 94

L represents a Lewis base such as amido- or phosphanido- anions or neutral Lewis bases such as ethers, amines and phosphanes.

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Scheme 3.18: Addition of diphenylphosphane to the singly hydroaminated molecules, [12], [13] and [*]. [*] is 1-diphenylamino-1,4-diphenylbut-1-ene-3-yne.

This work was published in 2016.[186]

Summary and perspective (English version)| 95

4 Summary and perspective (English version)

This thesis confirms that the addition reactions of various primary and secondary amines K\GURDPLQDWLRQ  DV ZHOO DV GLSKHQ\OSKRVSKDQH K\GURSKRVSKDQ\ODWLRQ  DFURVV WKH &Ł& triple bonds of diphenylbutadiyne can efficiently be catalyzed by a calciate complex. This calciate catalyst is a rival to the previously reported catalysts, such as those of d-orbital metals, lanthanoides and actinoides, which are mentioned in the introduction of the thesis. Importantly, the hydroamination and hydrophosphanylation reactions take place regioselectively whereas the latter occurs in a stereoselective manner. At the beginning of this work we were focusing on the modification of the complex-hexamethyldisilazide

[(L)2Ca{N(SiMe3)2}2] regarding to the coligand L and the possibility to apply the modified complex as catalyst. However, the latter complex for L = thf and L = thp was not sufficient to catalyze hydroamination reactions of diphenylbutadiyne with primary or secondary arylamines. The halide-free tetrahydropyran adduct [(thp)2Ca{N(SiMe3)2}2] ([1]) is easily available in single-crystalline form via transmetalation of tin(II)- bis[bis(trimethylsilyl)amide] with calcium metal and subsequent recrystallization from n-hexane. This colorless complex shows good solubility in common organic solvents. The molecular structure is dominated by steric factors as also observed for adducts of CaI2 and arylcalcium iodides.

Figure 4.1: [(thp)2Ca{N(SiMe3)2}2] ([1]).

Summary and perspective (English version)| 96

A slight elongation of the Ca-N and Ca-O bonds in comparison to the thf adducts is observed because the smaller ether thf also represents the stronger base. This bond elongation allows to reduce the N-Ca-N bond angle in [1] in comparison to [(thf)2Ca{N(SiMe3)2}2], thus reducing the strain between the thp ligands and the amido anions. The fact that homometallic calcium bis(amide) does not mediate hydroamination reactions raises the question of the cooperation of potassium and calcium in the catalyst system. This complex can be prepared by a two steps reaction. Metalation of 2,6-diisopropylaniline with

K[N(SiMe3)2] at higher temperature yields the corresponding potassium salt K{N(H)Dipp}.

Then, the metathetical approach of the excess of this potassium salt with CaI2 in THF leads [162b] to the formation of solvent-free calciate [K2Ca{N(H)Dipp}4]’[2].

Figure 4.2: Section of the polymeric structure of [2].

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Summary and perspective (English version)| 97

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WKH DON\QH PRLHWLHV LV WKH UHDVRQ WKDW .>&D^1 + 'LSS`@ >@  UHSUHVHQWV DQ LGHDO SUHFDWDO\VW IRU DQ\ K\GURIXQFWLRQDOL]DWLRQ RI GLSKHQ\OEXWDGL\QH ZLWK VWHULFDOO\ OHVV GHPDQGLQJSULPDU\RUVHFRQGDU\DU\ODPLQHVDVZHOODVGLSKHQ\OSKRVSKDQH,QDGGLWLRQWKLV FDOFLDWH LV VROXEOH LQ HWKHUHDO VROYHQWV HQDEOLQJ WKH SUHSDUDWLRQ RI VWRFN VROXWLRQV 7KH FU\VWDOOLQHFRPSRXQGDVZHOODVWKHVWRFNVROXWLRQVRIWKLVFRPSOH[DUHVWDEOHDQGFDQEH VWRUHGXQGHUDQDHURELFFRQGLWLRQV Using of the catalyst [2] to mediate the addition of primary arylamines (Figure 3.3) across the diyne backbone under kinetic control (at room temperature) leads to the unique formation of unsaturated seven-membered rings, depending on the ortho substituents of the arylamines (Figure 4.3 [3], [4], [5] and [6]). In contrast, the hydroamination of the same primary arylamines (Figure 3.3, a, b, c, e, and f) under thermodynamic control (in boiling THF) yields N-aryl-2,5-diphenylpyrroles regardless of the bulkiness of the N-bond aryl groups (Figure 4.3, [7], [8], [9], [10] and [11]).

Summary and perspective (English version)| 98

Figure 4.3: Hydroaminated diphenylbutadiyne by primary arylamines.

Summary and perspective (English version)| 99

The precatalyst K2[Ca{N(H)Dipp}4] was also used to study the hydroamination of diphenylbutadiyne with secondary arylamines. Using of secondary arylamines lead us to the less complicated products. After approximately 6 h a nearly complete conversion with a catalyst loading of 5 mol-% yields singly hydroaminated butadiyne. Diverse para- substituents such as H, Me and F were tested and gave the desired hydroamination products (N-methyl)-(N-aryl)-1,4-diphenylbut-1-ene-3-yne-1-ylamine of the type [Ph-&Ł&-CH=C

(Ph)]N(Me)(C6H4-4-R) with R = H [12], Me [13] and F [14]. This hydroamination was regioselective; however, both stereoisomers with E- and Z-arrangement at the C=C double bond were formed. The second calcium mediated K\GURDPLQDWLRQVWHSRIWKHRWKHU&Ł& triple bond which has not been reported before, requires much longer time at similar reaction conditions. After three days mixtures of singly and doubly hydroaminated diphenylbutadiyne were obtained if N-methylaniline was employed and complete doubly hydroaminated diphenylbutadiyne was obtained if N-methyl-4-fluoroaniline was employed. In contrast to this finding, no significant amounts of doubly hydroaminated diphenylbutadiyne was observed in the NMR spectra for the hydroamination with N-methyl- 4-tolylamine. Again, the catalytic hydroamination gave regioselectively 1,4-diphenyl-1,4- bis(N-methylanilino)buta-1,3-diene [15] and [16] but a mixture of E,E-, E,Z- and Z,Z- stereoisomers were obtained. The extremely decelerated second hydroamination allowed the isolation of pure singly hydroaminated diphenylbutadiyne. The catalytic hydroamination of [12] with N-methyl-4-fluoroaniline yielded exclusively the mixed doubly hydroaminated product [17] as a stereoisomeric mixture. The absence of [15] and [16] verifies that an amination-deamination equilibrium can be excluded.

Summary and perspective (English version)| 100

Figure 4.4: Products of singly and doubly hydroaminated diphenylbutadiyne by secondary arylamines.

The X-ray structures of E-isomeric [12], [13] and [14] suggest that the lone pair of the QLWURJHQDWRPVVKRZRQO\DYHU\VPDOOLQWHUDFWLRQZLWKWKHʌ-systems of the adjacent C=C double bonds whereas no delocalization into the N-bound aryl groups can be substantiated. The second amino group enhances steric strain and in Z,Z-isomeric [15], [16] and [17] the ORQHSDLUVRIWKHQLWURJHQDWRPVVOLJKWO\LQWHUDFWZLWKWKHʌ-systems of the N-bound aryl groups. This observation suggests that steric reasons might account for the significantly slower second hydroamination step.

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Summary and perspective (English version)| 101

Figure 4.5: Products of hydropentelation of diphenylbutadiyne by secondary amines and phosphane.

In the near future the focusing point will be on the control of the stereo- and regio- selectivity of hydropentelation reactions. We assume that these objectives can be achieved via protection of the catalytic center by bulky groups. Hence, we will investigate compound [6] in the transamination reaction with [Ca{N(SiMe3)2}] (Scheme 4.1) because it contains the novel E-diketimine unit. Simple E-diketiminate complexes have already been successfully used to catalyze hydroamination and hydrophosphanylation reactions as mentioned in the introduction part.

Scheme 4.1: Proposed scheme for transamination of [(L)2Ca{N(SiMe3)2}].

Zusammenfassung (Deutsche Version)| 102

5 Zusammenfassung (Deutsche Version)

Aus der vorliegenden Arbeit geht hervor, dass Additionsreaktionen von diversen primären und sekundären Aminen (Hydroaminierung) sowie von Diphenylphosphan +\GURSKRVSKDQ\OLHUXQJ  DQ &Ł& Dreifachbindungen von 1,4-Diphenylbutadiin auf effiziente Weise durch ein amid-basiertes Kalium-Calciat katalysiert werden können. Diese heterobimetallische Komplexverbindung steht in Konkurrenz zu etablierten Übergangsmetall- und Lanthanoid- basierten Katalysatoren, die in der Einleitung der Dissertation erwähnt werden. Es ist von Bedeutung, dass die hier untersuchten Hydroaminierungen und -phosphanylierungen regioselektiv stattfinden und die Hydrophos- phanylierung zusätzlich eine Stereoselektivität aufweist. Zu Beginn dieser Arbeit lag der

Fokus auf der Modifikation des Calcium-hexamethyldisilazids [(L)2Ca{N(SiMe3)2}2] hinsichtlich der Koliganden L und einer daraus resultierenden potentiellen Nutzbarkeit für katalytische Anwendungen. Allerdings konnte letztere für L = thf und L = thp bezüglich einer Hydroaminierung nicht nachgewiesen werden. Das halogenfreies Addukt

[(thp)2Ca{N(SiMe3)2}2] ([1]) ist in einkristalliner Form über die Transmetallierung von Zinn(II)-bis[bis(trimethylsilyl)amid] mit metallischem Calcium und anschließender Umkristallisation aus n-Hexan leicht verfügbar. Diese farblose Komplexverbindung zeigt eine gute Löslichkeit in gängigen organischen Lösungsmitteln. Die Veränderung der strukturellen Eigenschaften des THP-Adduktes im Vergleich zum THF-Addukt wird durch den vergrößerten sterischen Anspruch des THP dominiert, was auch bei THP-Addukten von

CaI2 und Arylcalciumiodid beobachtet wurde.

Abbildung 5.1: [(thp)2Ca{N(SiMe3)2}2] ([1]).

Zusammenfassung (Deutsche Version)| 103

Im Vergleich zu dem THF-Addukt wird eine leichte Verlängerung der Ca-O-Bindungen beobachtet, was mit der geringeren Nucleophilie des THP einhergeht. Der vergrößerte sterische Anspruch des THP veranlasst eine Verringerung des N-Ca-N-Bindungswinkels in

[1] im Vergleich zu [(thf)2Ca{N(SiMe3)2}2], wodurch die Spannung zwischen den THP- Liganden und den Amid- Anionen reduziert wird. Die Tatsache, dass das Calcium-bis(amid) Hydroaminierungsreaktionen nicht vermitteln konnte, wirft die Frage nach der Kooperation von Kalium und Calcium in dem hier verwendeten Katalysatorsystem [2] auf. Dieser Komplex kann durch eine zweistufige

Reaktion hergestellt werden. Die Metallierung von 2,6-Diisopropylanilin mit K[N(SiMe3)2] bei 100 °C ergibt das entsprechende Kaliumsalz K[N(H)DIPP], welches anschließend in einer Salzmetathese mit CaI2 in THF zum lösungsmittelfreien Calciat [K2Ca{N(H)DIPP}4]’ [2] umgesetzt wird.

Abbildung 5.2: Ausschnitt der polymeren Struktur von [2]. Es wird angenommen, dass die Isopropyl-Gruppen in ortho-Position die Anlagerung von Ko-Liganden wie Ethermoleküle verhindern. Im kristallinen Zustand bildet 2- K2[Ca{N(H)Dipp}4] ein Koordinationspolymer, bestehend aus [Ca{N(H)Dipp}4] Anionen, welche durch Kaliumkationen unter Ausbildung von K-S-Wechselwirkungen miteinander verbrückt werden. In diesen Calciat-Anionen, welche in Lösung erhalten bleiben, sind elektrostatische Abstoßungen zwischen den Amiden für eine Erhöhung der Ca- N-Bindungslängen und somit der Nucleophilie und Reaktivität verantwortlich. Über den

Zusammenfassung (Deutsche Version)| 104

Anteil der Reaktivitätssteigerung durch die Kaliumionen kann bislang nur spekuliert werden. Kaliumionen sind als weiche Lewis-Säuren in der Lage, an harte (z.B Ether) sowie vorzugsweise an weiche Lewis-Basen, wie Aromaten und ausgedehnte ʌ-Systeme zu koordinieren. Allerdings bleibt es bisher ungeklärt, was der Beitrag des Koordinationsverhaltens von K+ z.B. zu der Stabilisierung eines Übergangszustandes in der Hydroaminierung ist. Die Bildung der etherfreien Struktur im festen Zustand erleichtert die Handhabbarkeit, welche bei Ether-Addukten nicht gegeben ist, da die teilweise Freisetzung jener Koliganden zu Gewichtsverlust führen kann. Dies könnte eine genaue Einwaage und somit das Treffen der korrekten Stöchiometrie verhindern. Auf der anderen Seite erhöhen die Isopropylgruppen die intramolekulare sterische Spannung, was zu einer schnellen Substitution des 2,6-Diisopropylanilid- Anions durch kleinere Amid oder Phosphanid Liganden führt. Dieser anfängliche Amid oder Phosphanid-Austausch, welcher viel schneller als die Addition an die Alkin-Einheiten ist, ist der Grund dafür, dass

K2[Ca{N(H)DIPP}4] ([2]) einen idealen Präkatalysator für die Hydrofunktionalisierung von Diphenylbutadiin mit sterisch weniger anspruchsvollen primären oder sekundären Arylaminen sowie Diphenylphosphan darstellt. Darüber hinaus ist dieses Calciat in etherischen Lösungsmitteln löslich, was die Herstellung von Stammlösungen ermöglicht. Die kristalline Verbindung sowie die Stammlösungen dieses Komplexes sind stabil und können unter anaeroben Bedingungen aufbewahrt werden. Die Addition von primären, ortho- substituierten Arylaminen (Figure 3.3) an das Diin- Rückgrat unter Verwendung des Katalysators [2] führt unter kinetischer Kontrolle (bei Raumtemperatur) zu der spezifischen Bildung ungesättigter Siebenringe (Abbildung 5.3 [3], [4], [5] und [6]). Im Gegensatz dazu führt die Hydroaminierung der gleichen primären Arylamine (Figure 3.3, a, b, c, e, und f) unter thermodynamischer Kontrolle (in siedendem THF) zu N-Aryl-2,5-diphenylpyrrolen unabhängig vom sterischen Anspruch der N- gebundenen Arylgruppen (Abbildung 5.3, [7], [8], [9], [10] und [11]).

Zusammenfassung (Deutsche Version)| 105

Abbildung 5.3: Mit prämieren Aminen hydroaminiertes Diphenylbutadiin.

Zusammenfassung (Deutsche Version)| 106

Der Präkatalysator K2[Ca{N(H)DIPP}4] wurde außerdem zur Addition von sekundären N-Methyl- Anilinen an Diphenylbutadiin verwendet, woraufhin wesentlich unkompliziertere Produkte erhalten wurden. Bei einer Reaktionszeit von 6 h bei Raumtemperatur und einer Katalysatorbeladung von 5 mol-% kann ein nahezu vollständiger Umsatz zu einfach hydroaminierten Produkten beobachtet werden. Diverse para- substituierte Aniline (H, Me, F) führten mit sehr guten Ausbeuten zum vergleichbaren (N-methyl)-(N-aryl)-1,4- diphenylbut-1-en-3-in-1-ylaminen des Typs [Ph&Ł&CH=C(Ph)]N(Me)(C6H4-4-R) mit R = H [12], Me [13] und F [14]. Diese Reaktionen verliefen regioselektiv, jedoch nicht stereoselektiv, was die Bildung von E- und Z- Isomeren mit sich bringt. Die Hydroaminierung der verbliebenen Dreifachbindung findet bei gleichen Bedingungen allerdings erst nach langen Reaktionszeiten statt, was als Resultat aus der Erhöhung des sterischen Drucks der zweiten Aminofunktion anzusehen ist. Nach drei Tagen konnte im Fall von N- Methylanilin ein Gemisch aus einfach und doppelt hydroaminierten Produkten ([12] und [15]) und im Fall von N-Methyl-4-fluoranilin ein vollständiger Umsatz zum 1,4- Diphenyl-1,4-bis(N-methyl-4-fluoranilino)buta-1,3-dien ([16]) festgestellt werden. Diese Produkte liegen allerdings als Gemisch aus E,E-, E,Z- und Z,Z- Isomeren vor. Im Fall von N-Methyl-4tolylanilin fand hingegen keine zweite Addition statt. Der extrem verzögerte zweite Additionsschritt ermöglicht es, das einfach hydroaminierte Produkt zu isolieren und nachträglich zu funktionalisieren. So konnte [12] mit N-Methyl-4-fluoranilin zum gemischt doppelt hydroaminierten [17] umgesetzt werden. Da das Reaktionsgemisch keine Spuren von [15] und [16] enthält, kann ein Aminierungs-Deaminierungs-Gleichgewicht ausgeschlossen werden.

Zusammenfassung (Deutsche Version)| 107

Abbildung 5.4: Produkte von einfach und doppelt hydroaminiertem Diphenylbutadiin durch sekundäre Arylamine.

Die Molekülstrukturen der E-Isomere von [12], [13] und [14] verdeutlichen, dass das freie Elektronenpaar am Stickstoffatom nur sehr schwach mit dem S-System der benachbarten C=C Doppelbindungen interagiert und keine Delokalisation in die N-gebundenen Arylgruppen stattfindet. In den doppelt hydroaminierten Produkten [15], [16] und [17] ist dies auch der Fall.

Abschließend konnte gezeigt werden, dass durch den Präkatalysator K2[Ca{N(H)DIPP}4] auch Additionen von Diphenylphosphan an die (N-methyl)-(N-aryl)-1,4-diphenylbut-1-en- 3-in-1-ylamine [12], [13] und [*] ([*] ist 1-Diphenylamino-1,4-diphenylbut-1-en-3-in-1- ylamine) katalysiert werden können. Dies ermöglichte die Isolierung der Verbindungen [18], [19] und [20], wobei die Hydrophosphanylierung regio- und stereoselektiv abläuft.

Zusammenfassung (Deutsche Version)| 108

Abbildung 5.5: Produkte der Hydropentelation von Diphenylbutadiin mit sekundären Aminen und Phosphan.

Experimental part| 109

6 Experimental part

General remarks: All manipulations were carried out under an inert nitrogen atmosphere using standard Schlenk techniques. The solvents were dried over KOH and subsequently distilled over sodium/ benzophenone under a nitrogen atmosphere prior to use. Methanol was dried over magnesium pieces and methylene chloride over CaH2 and stored over molecular sieve 3Å. Deuterated solvents were dried over sodium, degassed, and saturated with nitrogen. 1H, 13C{1H}, 31P and 19F NMR spectra were recorded on Bruker AC 200 AC 400 and AC 600 spectrometers. Chemical shifts are reported in parts per million relative to DDS (4,4- 1 13 dimethyl-4-silapentane-1-sulfonic acid) for the H and C{1H} NMR measurements, D3PO4 31 31 19 (Phosphoric acid-d3) for P and P{1H} NMR measurements and trifluorotoluene for F NMR measurements as external standard. The residual signals of the deuterated solvents

[D8]THF, CDCl3 and CD2Cl2 were used as internal standards. All substrates were purchased from Sigma Aldrich, Merck or Alfa Aesar and used after distillation, only diphenylbutadiyne has been used without further purification. Mass spectra were obtained on a Finnigan MAT SSQ 710. IR spectra were recorded on the Perkin Elmer FT-IR-Spectrometer System 2000 as Nujol mulls between KBr windows and on a ATR-IR spectrometer. Elemental analysis on a LECO CHNS-932 apparatus gave values for C, H, N, and S. X-Ray structure determination. The intensity data for the compounds were collected on a

Nonius-Kappa-CCD diffractometer using graphite-monochromated Mo-KD radiation. Data were corrected for Lorentz and polarization effects; absorption was taken into account on a semi-empirical basis using multiple-scans.[187] The structures were solved by Direct Methods 2 [188] (SHELXS) and refined by full-matrix least squares techniques against Fo (SHELXL-97). The hydrogen atoms (with exception of methyl groups) were located by difference Fourier synthesis and refined isotopically. All non-hydrogen atoms were refined anisotropically.[188] Crystallographic data as well as structure solution and refinement details are already published.[162b, 164, 182, 184, 186] The program XP (SIEMENS Analytical X-ray Instruments, Inc.)[189] and POV-Ray were used for structure representations.[190]

Experimental part| 110

6.1 Unpublished result

6.1.1 Synthesis of N-(2,6-diisoprpylphenyl)-2,5-diphenylpyrrole [10]

Diphenylbutadiyne (0.25 g 1.23 mmol) was dissolved in 17 mL of THF before 2,6 diisopropylaniline (0.219 g, 1.23 mmol) and 10 mol-% of the calciate

K2[Ca{N(H)Dipp}4]’ (5 mol-% at the beginning and 5 mol-% after 3 d) were added and the reaction mixture heated for 6 d at 60 °C. Thereafter, the solution was hydrolyzed with 15 mL of distilled water, extracted with diethyl ether and the separated ether phase dried with sodium sulfate. Recrystallization from pentane at 5 °C yielded a colorless solid (0.34 g, 0.89 mmol, 72.8 %) in an orange mother 1 liquor. M.P. 165.5°C. H NMR (400 MHz, CDCl3) į 7.62 -7.58 (m, 4H, Ar-H), 7.44 - 7.21 3 (m, 9H, Ar-H), 7.11 - 7.09 (s, 2H), 3.36 - 3.21 (hept. 2H, JH,H = 6.8 Hz, CH), 1.44 - 0.89 (d, 3 13 JH,H = 6.8 Hz, 12H, CH3). C NMR (101 MHz, CDCl3) į 148.21 (C6), 145.82 (C1, C1A), 138.5, 134.8, 132.9, 132.9, 131.5, 130, 129.5, 129.1, 128.8, 128.3, 128, 127.6, 127.3, 126.7, 112.3, 111.6 (C2, C2A), 27.8 (C13, C13A), 25.87 (C14, C15, C14A, C15A). MS [EI, m/z (%)]: 378 (70) [M]+, 379 (100) [M], 313(40), 260 (20), 191 (10), 77 (10) [Ph]. IR 3064 w, 3028 w, 2912 w, 1702 w, 1599 m, 1542 w, 1482 s, 1388 m, 1336 m, 1299 m, 1076 m, 1027 m, 862 s, 786 m, 761 s, 746 vs, 691 vs, 619 s, 603 m, 508 m.

Experimental part| 111

6.2 Published results Compound Compound name Literature number [1] Bis(tetrahydropyran)Calcium Bis[bis(trimethylsilyl)amide] [164] [2] Dipotassium-tetrakis(diisoprobylanilido)calciate [162b] [3] 2-(tert-Butyl)-6,7,10,11-tetraphenyl-9H-cyclohepta[c]quinoline [182] [4] 2-(Fluoro)-6,7,10,11-tetraphenyl-9H-cyclohepta[c]quinoline [182] [5] 2,6-Diisopropyl-9,11,14,15-tetraphenyl-8- [182] azatetracyclo[8.5.0.01,7.02,13]pentadeca-3,5,7,9,11,14-hexaene [6] N-Mesityl-7-(E)-((mesitylimino)(phenyl)methyl)-2,3,6- [182] triphenylcyclohepta-1,3,6-trienylamine [7] N-(4-Tert-Butyl)phenyl)-2,5-diphenylpyrrole [182] [8] N-(4-Fluorophenyl)-2,5-diphenylpyrrole [182] [9] N-Mesityl-2,5-diphenylpyrrole [182] [10] N-(2,6-Diisoprpylphenyl)-2,5-diphenylpyrrole this work [11] N-Phenyl-2,5-diphenylpyrrole [182] [12] 1-(N-Methyl-anilino)-1,4-diphenylbut-1-ene-3- yne [184] [13] 1-(N-Methyl-para-toluidino)-1,4-diphenylbut-1-ene-3- yne [184] [14] 1-(N-Methyl-para-fluoroanilino)1,4-diphenylbut-1-ene-3-yne [184] [15] 1,4-di(N-Methyl-anilino)-1,4-diphenylbuta-1,3-diene [184] [16] 1,4-di(N-Methyl-4-fluoroanilino)buta-1,4-Diphenyl-1,3-diene [184] [17] 1-(N-Methyl-anilino)-4-( N-methyl-para-fluoroanilino) 1,4- [184] diphenylbut-1,3-diene [18] 1-(Diphenylphosphanyl)-1,4-diphenyl-4-(diphenylamino)buta-1,3- [186] diene [19] 1-(Diphenylphosphanyl)-1,4-diphenyl-4-(N-methyl-anilino)buta- [186] 1,3-diene [20] 1-(Diphenylphosphanyl)-1,4-diphenyl-4-(N-methyl-tolylamino)- [186] buta-1,3-diene

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8 Attachment

Attached publications

1. Fadi M. Younis, Helmar Görls, Sven Krieck, Matthias Westerhausen. Synthesis and structural characterization of bis(tetrahydropyran)calciumbis[ bis(tri-methylsilyl)amide]. Z. Anorg. Allg. Chem. 2013, 19-21 2. Carsten Glock, Fadi M. Younis, Steffen Ziemann, Helmar Görls, Wolfgang Imhof, Sven Krieck, Matthias Westerhausen. 2,6-Diisopropylphenylamides of Potassium and Calcium A Primary Amido Ligand in s-Block Metal Chemistry with an Astonishing Reactivity. Organometallics 2013, 32, 2649- 2660 3. Fadi. M. Younis, S. Krieck, H. Görls, M. Westerhausen. S-Block-Metal- Mediated Hydroamination of Diphenylbutadiyne with Primary Arylamines Using a Dipotassium Tetrakis(amino)calciate Precatalyst. Organometallics 2015, 34, 3577-3585. 4. Fadi. M. Younis, S. Krieck, H. Görls, M. Westerhausen. Hydroamination of diphenylbutadiyne with secondary N-methyl-anilines using the dipotassium tetrakis(2,6-diisopropylanilino)calciate precatalyst. Dalton Trans., 2016, 45, 6241-6250. 5. Fadi. M. Younis, S. Krieck, T.M. A. Al-shboul, H. Görls, M. Westerhausen. Calcium-Mediated Catalytic Synthesis of 1-(Diorganylamino)-1,4-diphenyl- 4-(diphenylphosphanyl)buta-1,3-dienes. Inorg. Chem. 2016, 55, 4676-4682.

SHORT COMMUNICATION

DOI: 10.1002/zaac.201200443

Synthesis and Structural Characterization of Bis(tetrahydropyran)calcium Bis[bis(trimethylsilyl)amide]

Fadi M. Younis,[a] Helmar Görls,[a] Sven Krieck,[a] and Matthias Westerhausen*[a]

Keywords: Calcium; Amides; Transmetalation; Bis(trimethylsilyl)amide; Tetrahydropyran

Abstract. Transmetalation of Sn[N(SiMe3)2]2 with calcium granules lengths of 231.08(11) and 240.23(9) pm, respectively. The molecular in tetrahydropyran (thp) yields colorless [(thp)2Ca{N(SiMe3)2}2](1) structure is dominated by steric factors leading to a NCaN bond angle which is soluble in common organic solvents. The calcium center is of 119.43(6)°. in a distorted tetrahedral environment with Ca–N and Ca–O bond

Introduction Results and Discussion

The initial synthesis of the bis(trimethylsilyl)amides of the Due to the tremendous importance of Ca[N(SiMe3)2]2 in or- heavier alkaline earth metals by various methods approxi- ganocalcium chemistry many base adducts were prepared and mately twenty years ago offered a valuable reagent for a fruit- structurally characterized. The tetrahydrofuran complex is the ful organocalcium chemistry because these amides are soluble favored synthon for this chemistry, however, this ether exhibits in common organic solvents.[1–4] The major access routes in- ring strain and therefore ether cleavage can occur quite easily [5–7] during metal-organic transformations. Therefore, we investi- clude salt-metathesis reactions of KN(SiMe3)2 with CaI2, [8] [9] gated the tetrahydropyran adduct of Ca[N(SiMe3)2]2. In order transmetalation of M[N(SiMe3)2]2 with Ca (M = Hg, Sn ) to obtain halide-free [(thp)2Ca{N(SiMe3)2}2](1) we have cho- and direct metalation of HN(SiMe3)2 with calcium in the pres- [10] [11] [12] sen the transmetalation of freshly distilled Sn[N(SiMe3)2]2 ence of ammonia or BiPh3. Recently, Johns et al. showed that the salt-metathesis reactions can yield with calcium granules according to Equation (1). During this heterogeneous reaction the color of the solution turned reddish Ca[N(SiMe3)2]2 that is contaminated with KN(SiMe3)2 and therefore they recommend metalation of the amine with di- brown. After filtration the solvent was removed in vacuo and the residue recrystallized from n-hexane yielding pure 1. benzylcalcium. The popularity of Ca[N(SiMe3)2]2 in s-block metal chemistry is based on easy preparative procedures, solu- bility in common organic solvents, non-toxicity of the metals, tunability of the reactivity by various methods such as varia- (1) tion of the bulkiness of substituents or the base strength of the solvent. In addition, the conversion to alkali metal tris(amido) calciates[13–15] or calcium metalates (e.g. zincates[16]) represent The molecular structure and the numbering scheme are dis- concepts to alter the reactivity of these amides.[17] played in Figure 1. The tetra-coordinate metal atom is in a The calcium–nitrogen bonds in calcium bis(amides) show a severely distorted tetrahedral coordination sphere with a large highly ionic nature and the bonding situation is dominated by N1–Ca1–N1A angle of 119.4°. The nitrogen atoms are in dis- electrostatic attraction between the cation and the anions as torted trigonal planar environments with an average N–Si bond well as repulsive forces between anions. Thus, the bulkiness of 168.9 pm. This short bond is characteristic for of the ligands plays a prominent role with respect to the coor- bis(trimethylsilyl)amides bound at electropositive s-block dination number of calcium. In addition, Ca2+ represents a metals[18] because the hyperconjugation of negative charge σ Lewis acid forming adducts with Lewis bases. Thus a coordi- from the pz(N) orbital into *(Si–C) orbitals strengthens the nation number of three requires bulky bases as, for example, N–Si bonds. The bulkiness of the trimethylsilyl groups en- in tris[bis(trimethylsilyl)amido]calciates.[13–15] forces a large Si1–N1–Si2 bond angle. In order to evaluate structural characteristics, mononuclear calcium bis[bis(silyl)amides] are summarized in Table 1. The * Prof. Dr. M. Westerhausen Fax: +49-3641-948102 compounds are arranged according to the coordination number E-Mail: [email protected] of the calcium atom [CN (Ca)] and within these groups accord- [a] Institut für Anorganische und Analytische Chemie ing to the Ca–N distances. It is obvious that bulkier silyl sub- Friedrich-Schiller-Universität Humboldtstrasse 8 stituents lead to elongated Ca–N bonds which vary between 07743 Jena, Germany 227 and 239 pm. The Ca–L distances (the donor atoms are

Z. Anorg. Allg. Chem. 2013, 639, (1), 19–21 © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 19 SHORT COMMUNICATION F. M. Younis, H. Görls, S. Krieck, M. Westerhausen

contacts of the calcium atom to trimethylsilyl groups addition- ally shield the metal atom. In general, the N–Ca–N bond angles are large due to steric repulsion between the bulky bis(silyl)amido ligands and due to electrostatic repulsion between the anions. The smallest value

is observed for [(thp)2Ca{N(SiMe3)2}2](1) because tetra- hydropyran is a rather demanding cyclic ether. Larger co-li- gands enhance the intramolecular steric strain whereas longer Ca–L bonds lead to strain relaxation. In comparison to the thf

adduct [(thf)2Ca{N(SiMe3)2}2], the weaker base thp leads to longer Ca–O bonds. However, the bulkier ether thp also leads to a slight elongation of the Ca–N bonds and to a rather small N–Ca–N angle. Often complexes containing this cyclic ether ligands exhibit advantageous crystallization behavior in com- parison to thf adducts because thf ligands tend to show large thermal motion and disordering in the solid state.[27,28] Figure 1. Molecular structure and numbering scheme of [(thp)2Ca{N(SiMe3)2}2](1). The ellipsoids represent a probability of 40%, hydrogen atoms are neglected for clarity reasons. Symmetry- Conclusions related atoms (–x+1, y,–z+0.5) are marked with the letter “A”. Selected bond lengths /pm: Ca1–N1 231.1(1), Ca1–O1 240.2(1), N1–Si1 The halide-free tetrahydropyran adduct [(thp)2Ca{N(SiMe3)2}2] 168.8(1), N1–Si2 169.0(1), Ca1···C6 318.2(2), Ca1···Si1 346.6(1), (1) is easily available in single-crystalline form via transmet- Ca1···Si2 334.4(1); angles /deg: N1–Ca1–N1A 119.4(1), N1–Ca1–O1 alation of tin(II) bis[bis(trimethylsilyl)amide] and subsequent 94.3(1), N1–Ca1–O1A 134.9(1), O1–Ca1–O1A 78.6(1), Ca1–N1–Si1 119.3(1), Ca1–N1–Si2 112.5(1), Si1–N1–Si2 128.2(1). recrystallization from alkanes. This colorless complex shows good solubility in common organic solvents. The molecular structure is dominated by steric factors as also observed for [27] given in brackets) strongly depend on the donor base because adducts of CaI2 and arylcalcium iodides. A slight the atomic radii decrease from C over N to O. However, the elongation of the Ca–N and Ca–O bonds in comparison major influence of these co-ligands on the Ca–N bond lengths to the thf adducts is observed because the smaller ether thf seems to be of steric nature. Even the coordination number of also represents the stronger base. This bond elongation calcium plays a minor role as can be seen from the complexes allows to reduce the N–Ca–N angle in 1 in comparison to [22] with three- and five-coordinate alkaline earth metal centers [(thf)2Ca{N(SiMe3)2}2] thus reducing the strain between showing Ca–N values well within the range for adducts with the thp ligands and the amido anions. Due to the fact that thp tetra-coordinate calcium atoms. Free coordination sites can be is a weaker and bulkier base than thf, a slightly enhanced shielded by agostic bonds to the trialkylsilyl groups as ob- reactivity of 1 might be expected in comparison to [20] served for [(thf)2Ca{N(SiMe3)(SiPh3)}2]. A detailed dis- [(thf)2Ca{N(SiMe3)2}2]. In addition, substitution of the rather cussion on such secondary bonds was provided by Ruhlandt- floppy thf by thp ligands, which adopt the chair conformation Senge and co-workers[4] (see also Ref. [26]). In 1, rather short in the solid state, often improves the crystallization behavior

Table 1. Comparison of selected structural parameters of mononuclear calcium bis[bis(silyl)amides] of the type [(L)Ca{N(SiR3)2}2] [average values, bond lengths /pm and angles /°, CN(Ca) coordination number of calcium; dme 1,2-dimethoxyethane, thf tetrahydrofuran, thp tetra- hydropyran, tBuIm N-tert-butylimidazole, tmeda tetramethylethylenediamine, py pyridine, dmap 4-dimethylaminopyridine, hmpa hexameth- ylphosphoric acid triamide).

L NSiR3 CN(Ca) Ca–N /pm Ca–L /pm N–Ca–N /° Ref.

NHC-1 N(SiMe3)2 3 229.0 259.8 (C) 125.4 [19] NHC-2 N(SiMe3)2 3 230.3 262.9 (C) 124.5 [19] thf N(SiMe3)(SiPh2tBu) 3 232.3 238.2 (O) 134.6 [20] dme N(SiMe3)2 4 227.1 239.7 (O) 123.6 [21] 2 thf N(SiMe3)2 4 230.2 237.7 (O) 121.3 [22] 2 thp N(SiMe3)2 4 231.2 240.2 (O) 119.4 This work 1 tmeda N(SiMe3)2 4 231.5 259.2 (N) 121.8 [23] 2 tBuIm N(SiMe3)2 4 232.5 246.4 (N) 123.3 [24] 2Ph3PO N(SiMe3)2 4 233.7 226.5 (O) 129.4 [19] 2 py N(SiMe3)(SiMe2tBu) 4 235.3 253.7 (N) 125.3 [20] a 2 thf N(SiMe3)(SiPh3) 4 236.0 237.3 (O) 146.6 [20] 2 dmap N(SiMe3)(SiMe2tBu) 4 236.7 249.8 (N) 122.3 [20] 2 hmpa N(SiMe3)(SiMe2tBu) 4 239.0 228.0 (O) 125.2 [20] b 3 thf N(SiMe2CH2)2 5 233.6 240.2 (O) 136.8 [25] a) Coordination number 4+2 due to two additional agostic interactions to trimethylsilyl groups; b) trigonal bipyramidal environment of calcium with the amido ligands in equatorial positions.

20 www.zaac.wiley-vch.de © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Z. Anorg. Allg. Chem. 2013, 19–21 Bis(tetrahydropyran)calcium Bis[bis(trimethylsilyl)amide] of metal complexes thus facilitating the isolation of crystalline [3] M. Westerhausen, J. Langer, S. Krieck, C. Glock, Rev. Inorg. and pure material. Chem. 2011, 31, 143–184. [4] A. Torvisco, A. Y. O’Brien, K. Ruhlandt-Senge, Coord. Chem. Rev. 2011, 255, 1268–1292. [5] P. S. Tanner, D. J. Burkey, T. P. Hanusa, Polyhedron 1995, 14, Experimental Section 331–333. [6] E. D. Brady, T. P. Hanusa, M. Pink, V. G. Young, Inorg. Chem. Synthesis: All procedures and manipulations of the compounds were 2000, 39, 6028–6037. performed in an anhydrous nitrogen atmosphere. The synthesis was [7] X. He, B. C. Noll, A. Beatty, R. E. Mulvey, K. W. Henderson, J. performed in analogy to a literature procedure.[9] The NMR spectra Am. Chem. Soc. 2004, 126, 7444–7445. were recorded at room temp. at [D6]benzene solutions. Calcium [8] D. C. Bradley, M. B. Hursthouse, A. A. Ibrahim, K. M. granules (0.5 g, 12.5 mmol) and 5,4 g (12,5 mmol) of tin(II) Abdul Malik, M. Motevalli, R. Möseler, H. Powell, J. D. Run- bis[bis(trimethylsilyl)amide] were combined in THP (50 mL). After a nacles, A. C. Sullivan, Polyhedron 1990, 9, 2959–2964. few hours the solution turned dark red. After 9 h stirring at room [9] M. Westerhausen, Inorg. Chem. 1991, 30, 96–101. temperature the reaction was finished and the color of the reaction [10] S. R. Drake, D. J. Otway, S. P. Perlepes, Main Group Met. Chem. 1991, 14, 243–256. mixture was reddish brown. Afterwards, the reaction mixture was fil- [11] M. M. Gillett-Kunnath, J. G. MacLellan, C. M. Forsyth, P. C. An- tered. The solvent of the filtrate was removed in vacuo and the residue drews, G. B. Deacon, K. Ruhlandt-Senge, Chem. Commun. 2008, recrystallized from n-hexane. At –5 C°, 3.8 g of colorless crystals 4490–4492. (7,1 mmol, 56,8%) precipitated that were suitable for X-ray diffraction [12] A. M. Johns, S. C. Chmely, T. P. Hanusa, Inorg. Chem. 2009, 48, studies. Physical data: M.p.: 149 °C. 1H NMR: δ = 0.37 (s, 18 H, 1380–1384.

SiMe3), 1.13 (m, 2 H, thp, p-CH2), 1.20 (m, 4 H, thp, m-CH2), 3.59 [13] X. He, J. F. Allan, B. C. Noll, A. R. Kennedy, K. W. Henderson, 13 1 J. Am. Chem. Soc. 2005, 127, 6920–6921. (m, 4 H, thp, o-CH2). C{ H} NMR: δ = 5.85 (SiMe3), 22.46 (thp, [14] X. He, E. Hurley, B. C. Noll, K. W. Henderson, Organometallics p-CH2), 25.95 (thp, m-CH2), 70.44 (thp, o-CH2). MS (EI): 161 (20%), 147 (50%), 146 (100%), 130 (70%), 86 (12 %, [thp]+). IR (Nujol, 2008, 27, 3094–3102. [15] M. S. Hill, G. Kociok-Köhn, D. J. MacDougall, Inorg. Chem. KBr windows): 1457 vs, 1377 s, 1310 w, 1251 vs, 1178 m, 1092 w, 2011, 50, 5234–5241. 1077 w, 1047 s, 967 w, 931 s, 883 sh, 842 s, 748 m, 683 w, 662 m, [16] M. Westerhausen, Z. Anorg. Allg. Chem. 1992, 618, 131–138. –1 606 w, 590 m, 571 m cm . Elemental analysis was impossible because [17] M. Westerhausen, Dalton Trans. 2006, 4755–4768. the mass of the substance was not constant during weighing and hand- [18] K. F. Tesh, T. P. Hanusa, J. C. Huffman, Inorg. Chem. 1990, 29, ling due to loss of ligand once isolated. 1584–1586. [19] A. G. M. Barrett, M. R. Crimmin, M. S. Hill, G. Kociok-Köhn, Structure Determination: The intensity data for the compounds was D. J. MacDougall, M. F. Mahon, P. A. Procopiou, Organometal- collected with a Nonius KappaCCD diffractometer using graphite-mo- lics 2008, 27, 3939–3946. nochromated Mo-Kα radiation. Data was corrected for Lorentz and [20] Y. Tang, L. N. Zakharov, W. S. Kassel, A. L. Rheingold, R. A. polarization effects but not for absorption effects.[29,30] The structures Kemp, Inorg. Chim. Acta 2005, 358, 2014–2022. [21] M. Westerhausen, W. Schwarz, Z. Anorg. Allg. Chem. 1991, 604, were solved by direct methods (SHELXS[31]) and refined by full-ma- 2 [31] 127–140. trix least-squares techniques against Fo (SHELXL-97 ). The hydro- [22] M. Westerhausen, M. Hartmann, N. Makropoulos, B. Wieneke, gen atoms were located by difference Fourier synthesis and refined M. Wieneke, W. Schwarz, D. Stalke, Z. Naturforsch. 1998, 53b, isotropically.[31] All non-hydrogen atoms were refined anisotropi- 117–125. cally.[29] XP (SIEMENS Analytical X-ray Instruments, Inc.) was used [23] C. Glock, H. Görls, M. Westerhausen, Inorg. Chim. Acta 2011, for structure representations. Crystal Data for 1:C22H56CaN2O2Si4, 374, 429–434. 533.13 g·mol–1, colorless prism, size 0.06 ϫ 0.06 ϫ 0.04 mm3, mono- [24] M. Arrowsmith, A. Heath, M. S. Hill, P. B. Hitchcock, G. Kociok- clinic, space group C2/c, a = 17.9171(3), b = 11.0021(2), c = Köhn, Organometallics 2009, 28, 4550–4559. 17.7543(4) Å, β = 107.312(1)°, V = 3341.28(11) Å3, T = –140 °C, Z = [25] M. Westerhausen, J. Greul, H.-D. Hausen, W. Schwarz, Z. Anorg. –3 –1 Allg. Chem. 1996, 622, 1295–1305. 4, ρ = 1.060 g·cm , μ(Mo-Kα) = 3.5 cm , F(000) = 1176, 10106 calcd. [26] Agostic bondings generally play an important role in the chemis- reflections in h(–22/23), k(–14/11), l(–23/23), measured in the range try of Lewis acidic d0 systems such as early transition metal cat- Յ Θ Յ Θ 3.51° 27.48°, completeness max = 99.7%, 3829 independent ions (e.g. Ti4+ and Zr4+); a recent perspective on this kind of reflections, Rint = 0.0243, 3431 reflections with Fo Ͼ 4σ(Fo), 253 pa- M···H–C interactions is given in: J. Saßmannshausen, Dalton rameters, 0 restraints, R1obs = 0.0309, wR2obs = 0.0737, R1all = 0.0361, Trans. 2012, 41, 1919–1923. wR2all = 0.0773, GOOF = 1.070, largest difference peak and hole: [27] J. Langer, S. Krieck, R. Fischer, H. Görls, M. Westerhausen, Z. 0.281/–0.183 e·Å–3. Anorg. Allg. Chem. 2010, 636, 1190–1198. [28] J. Langer, M. Köhler, R. Fischer, F. Dündar, H. Görls, M. West- Crystallographic data (excluding structure factors) has been deposited erhausen, Organometallics 2012, 31, 6172–6182. [29] COLLECT, Data Collection Software; Nonius B. V., Netherlands, with the Cambridge Crystallographic Data Centre as supplementary 1998. publication CCDC-903644 for 1. Copies of the data can be obtained [30] Z. Otwinowski, W. Minor, Processing of X-ray Diffraction Data free of charge on application to CCDC, 12 Union Road, Cambridge Collected in Oscillation Mode, in: Methods in Enzymology, Vol. CB2 1EZ, UK [E-mail: [email protected]]. 276, Macromolecular Crystallography, Part A (Eds.: C. W. Car- ter, R. M. Sweet), pp. 307–326, Academic Press: New York, 1997. References [31] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122. [1] M. Westerhausen, Trends Organomet. Chem. 1997, 2, 89–105. Received: October 2, 2012 [2] M. Westerhausen, Coord. Chem. Rev. 1998, 176, 157–210. Published Online: November 15, 2012

Z. Anorg. Allg. Chem. 2013, 19–21 © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 21 Article

pubs.acs.org/Organometallics

2,6-Diisopropylphenylamides of Potassium and Calcium: A Primary Amido Ligand in s‑Block Metal Chemistry with an Unprecedented Catalytic Reactivity † § † § † † ‡ † Carsten Glock, , Fadi M. Younis, , Steffen Ziemann, Helmar Görls, Wolfgang Imhof, Sven Krieck, † and Matthias Westerhausen*, † Institut für Anorganische und Analytische Chemie, Friedrich-Schiller-Universitaẗ Jena, Humboldtstrasse 8, D-07743 Jena, Germany ‡ Institut für Integrierte Naturwissenschaften, Abteilung Chemie, Universitaẗ Koblenz-Landau, Universitatsstrassë 1, D-56070 Koblenz, Germany

*S Supporting Information

ABSTRACT: Transamination of KN(SiMe3)2 with 2,6-diisopropylphenylamine (2,6-diisopropylaniline) in toluene at ambient temperature yields [K{N(H)- · Dipp} KN(SiMe3)2](1) regardless of the applied stoichiometry. Recrystallization of 1 in the presence of tetramethylethylenediamine (TMEDA) and tetrahydrofuran μ (THF) leads to the formation of [( -thf)K2{N(H)Dipp}2]∞ (2), whereas potassium bis(trimethylsilyl)amide remains in solution. Addition of pentamethyldiethylenetri- amine (PMDETA) gives [(pmdeta)K{N(H)Dipp}]2 (3). In contrast to the thf and pmdeta adducts, which lead to dissociation of 1 into homoleptic species, addition of μ bidentate dimethoxyethane maintains the mixed complex [(dme)K{ -N(SiMe3)2}- μ { -N(H)Dipp}K]2 (4). A complete transamination of 2,6-diisopropylaniline with ° KN(SiMe3)2 in toluene at 100 C yields [K{N(H)Dipp}] (5), which reacts with CaI2 to give [(thf)nCa{N(H)Dipp}2](6), [(pmdeta)Ca{N(H)Dipp}2](7), and [(dme)2Ca{N(H)Dipp}2](8), depending on the solvents and coligands. Excess potassium 2,6-diisopropylphenylamide allows the formation of the calciate [K2Ca{N(H)Dipp}4]∞ (9). Hydroamination of diphenylbutadiyne with 2,6-diisopropylaniline in the presence of catalytic amounts of 9 gives tetracyclic 2,6-diisopropyl- 9,11,14,15-tetraphenyl-8-azatetracyclo[8.5.0.01,7.02,13]pentadeca-3,5,7,9,11,14-hexaene (10). Solid-state structures are reported for 2−4 and 7−10. Compound 10 slowly rearranges to tetracyclic 5a,9-diisopropyl-2,3,10,11-tetraphenyl-5a,6-dihydro-2a1,6- ethenocyclohepta[cd]isoindole (11), which is slightly favored according to quantum chemical studies.

■ INTRODUCTION to these complexes, which are soluble in tetrahydrofuran Substituted amides of the electropositive s-block metals (THF), the 2,2,6,6-tetramethylpiperidylcalcium complexes express an enormous reactivity and cannot be handled in represent valuable reagents for diverse applications such as 9 metalation, transamination, and amide transfer. Whereas several THF because of ether degradation processes. In contrast to reviews exist discussing structures, properties, and reactivity of the case for stable amidomagnesium halides these Hauser-type alkali-metal amides,1 interest in organyl-substituted alkaline- bases of calcium show ligand redistribution processes (Schlenk- type equilibrium) favoring homoleptic calcium bis(amide) and earth-metal bis(amides) has been limited mainly to magnesium 10 derivatives for a long time.2 The homologous heavier alkaline- calcium dihalide. earth-metal complexes have attracted attention only for about Primary anilides of the heavier alkaline-earth metals tend to the last two decades.3,4 Early attempts gave insoluble, poorly form aggregates (Ca) or even polymers (Sr, Ba) in the solid characterized, and partially pyrophoric alkaline-earth-metal state and are only sparingly soluble in Lewis basic donor 11 fl amides.5 Approximately 20 years ago, the breakthrough solvents. 2,6-Di uoroanilides form more soluble complexes, but fluorine substituents in metal organic compounds may be succeeded with the synthesis of the alkaline-earth-metal 12 bis[bis(trialkylsilyl)amides], which are soluble in common hazardous and decompose spontaneously and violently. o- organic solvents such as ethers and aromatic and aliphatic Alkyl-substituted anilides form monomeric complexes with a hydrocarbons, allowing homogeneous reaction conditions.6 strongly Lewis basic coligand such as hexamethylphosphoric In recent years the portfolio of amides of the heavy alkaline- acid triamide (hmpa), and mononuclear complexes of the type earth metals Ae became versatile. Solubility was guaranteed by [(hmpa)3Ae{N(H)Dipp}2](Dipp=C6H3-2,6-iPr2)were isolated.3 substitution of only one trialkylsilyl group of Ae{N(SiMe3)2}2 by an aryl substituent, leading to substituted trimethylsilylani- lides.3,7 Recently also diphenylamides8 and N-alkylanilides9 Received: February 21, 2013 have been prepared and structurally characterized. In contrast Published: April 16, 2013

© 2013 American Chemical Society 2649 dx.doi.org/10.1021/om4001007 | Organometallics 2013, 32, 2649−2660 Organometallics Article

Scheme 1. Reaction Scheme for the Synthesis of Potassium, Calcium, and Mixed-Metal 2,6-Diisopropylanilides

fi μ μ Heterobimetallic s-block metal amides exhibit signi cantly etry and tetranuclear [(dme)K{ -N(SiMe3)2}{ -N(H)Dipp}- − enhanced reactivity. Mixed alkali-metal magnesium amides K]2 (4) was isolated. tend to form inverse crowns which react as highly reactive More drastic reaction conditions during transamination of 13 − metalation reagents, whereas the alkali-metal calcium KN(SiMe3)2 with H2N-Dipp gave solvent-free K{N(H)Dipp} derivatives can best be described as alkali-metal calciates due (5), which was used as an amide transfer reagent. The − to the amido transfer from the alkali metal to calcium.9,14 16 metathesis reaction of this potassium amide with calcium The awakened interest in these alkaline-earth-metal amides is diiodide yielded the oily substance [(thf)nCa{N(H)Dipp}2](6) also based on the catalytic activity (for recent general reviews in solvents such as THF, hexane, toluene, and mixtures thereof. see ref 17) in hydroamination reactions of carbodiimides,18 The addition of tridentate pmdeta or bidentate dme led to 19,20 16,20 alkenes, and alkynes. Especially calcium is a very crystalline [(pmdeta)Ca{N(H)Dipp}2](7) and [(dme)2Ca{N- attractive inexpensive element, due to its worldwide availability (H)Dipp}2](8), respectively. Excess potassium 2,6-diisopro- and nontoxicity regardless of the concentration. In many pylphenylamide yielded the calciate [K2Ca{N(H)Dipp}4]∞ (9), catalytic applications Ae{N(SiMe3)2}2 was employed as the which precipitated from a THF solution as a solvent-free precatalyst, intermediately forming the catalytically active coordination polymer. calcium amides. We could demonstrate that often highly The influence of the metals on the chemical 1H and 13C{1H} reactive heterobimetallic compounds such as potassium NMR shifts of the 2,6-diisopropylphenylamide ions is small and calciates are required to catalyze the addition of amines to seems to be not especially diagnostic of structure. Therefore, a carbon−carbon multiple bonds.16 detailed discussion is not included and the data are given in the Supporting Information. 2,6-Diisopropylaniline shows low- fi 1 ■ RESULTS AND DISCUSSION eld-shifted H NMR resonances of the aryl and amino hydrogen atoms. For the potassium derivatives these signals are Synthesis. Transamination of KN(SiMe3)2 with 2,6- high-field-shifted; however, the values of the calcium complexes diisopropylphenylamine (H2N-Dipp) in toluene at room are very similar. The tertiary CH fragments of the isopropyl temperature led to precipitation of [K{N(H)Dipp}·KN- groups show chemical shifts of δ 3.15 and 3.00 for the (SiMe3)2](1) regardless of the applied stoichiometry. The potassium and calcium anilides, respectively. formation of a solid precipitate impeded the complete In the 13C{1H} NMR spectra the largest differences are conversion to potassium 2,6-diisopropylphenylamide. Addition observed for the ipso-carbon atoms; deprotonation of 2,6- of Lewis bases often yields smaller and soluble aggregates which diisopropylaniline leads to a significant low-field shift. The allow spectroscopic characterization. Compound 1 was formation of heterobimetallic potassium tetrakis(anilido)- dissolved in a mixture of tetramethylethylenediamine calciate shifts the resonance of the ipso-carbon back toward a (TMEDA) and tetrahydrofuran (THF), and from this solution higher field. The influences of the metal and the environment μ crystals of [( -thf)K2{N(H)Dipp}2]∞ (2) precipitated, whereas of the amido functionality (terminal or bridging position) on potassium bis(trimethylsilyl)amide remained in solution the other carbon atoms are very small, and no dependency is (Scheme 1). A similar finding was observed upon addition of observed for the chemical shifts of the isopropyl groups. a solvent mixture of pentamethyldiethylenetriamine (PMDE- On the basis of NMR parameters structure elucidation is TA) and THF, yielding crystalline [(pmdeta)K{N(H)Dipp}]2 impossible. All s-block metal amides 1−9 show only one set of fi (3), whereas KN(SiMe3)2 remained in the mother liquor. In resonances with very similar chemical shifts. This nding is in contrast to the thf and pmdeta adducts, which led to agreement with the expectation that in ionic amides the nature dissociation of 1 into homoleptic species, addition of bidentate of the metal atoms plays an ancillary role. Dissociation of these 1,2-dimethoxyethane (DME) maintained the mixed stoichiom- complexes and fast dynamic behavior on the NMR time scale

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(thus breaking up polymeric structures) explain not only this observation but also solubility in common organic donor solvents. Due to the fact that information on solution structures is very limited, we investigated the solid-state structures in order to verify the formation of homometallic and mixed s- block metal amides and to study the influence of coordinated solvent molecules. Molecular Structures. Schematic representations are given in Scheme 1, and the molecular structures of the potassium amides 2−4, and the calcium bis(anilides) 7 and 8 as well as the coordination polymer 9 are discussed in detail. The molecular structure and numbering scheme of a section of polymeric 2 are shown in Figure 1. The central structural

Figure 2. Molecular structure and numbering scheme of 3. The ellipsoids represent a probability of 40%, and H atoms are omitted for clarity. The symmetry-equivalent half of the molecule (−x +2,−y, −z + 1) is marked with the letter A. Selected bond lengths (pm): K1−N1 = 291.6(3), K1−N1A = 279.4(3), K1−N2 = 289.2(3), K1−N3 = 296.9(3), K1−N4 = 318.3(3), N1−C1 = 136.3(4).

Figure 1. Section of polymeric 2. The ellipsoids represent a probability of 40%, and H atoms are neglected for clarity. Symmetry-related atoms are marked with the letters A−D. Selected bond lengths (pm): K1A− N1C = 277.9(2), K1A−N2B = 275.4(2), K1A−O1A = 294.7(2), K2A−N1C = 277.3(2), K2A−N2B = 275.2(2), K2A−O1A = 286.8(2), K1A−C1A = 318.2(2), K1A−C2A = 316.7(2), K1A−C3A = 314.8(2), K1A−C4A= 313.3(2), K1A−C5A = 313.3(2), K1A−C6A = 317.3(2), K2A−C13A = 315.0(2), K2A−C14A = 322.0(2), K2A− C15A = 320.9(2), K2A−C16A = 314.4(2), K2A−C17A = 306.8(2), K2A−C18A = 306.6(2), N1C−C1C = 135.6(2), N2B−C13B = 135.8(2). fragment consists of a four-membered K N ring (average K−N 2 2 Figure 3. Molecular structure and numbering scheme of 4. The distance 276.4 pm) with a bridging thf ligand between the ellipsoids represent a probability of 40%, and H atoms are neglected. potassium atoms. Thus, there exist three bridges between the − − − ··· The symmetry-related molecule halves ( x +2, y +1, z) are alkali-metal atoms, leading to a short K1 K2 contact of only distinguished by the letters A and B. Selected bond lengths (pm): 349.1(1) pm. The dinuclear units are aligned to a one- K1A−N1B = 274.2(1), K1A−N2A = 280.9(1), K2A−N1B = 276.3(1), dimensional strand via Lewis acid−base interactions between K2A−N2A = 274.3(1), K2A−O1A = 273.3(1), K2A−O2A = the soft potassium cations and the π systems of neighboring 276.2(1), K1A−C1A = 320.3(1), K1A−C2A = 326.2(1), K1A−C3A anilide moieties. = 323.5(2), K1A−C4A = 318.9(2), K1A−C5A = 315.3(2), K1A−C6A Enhancing the denticity and base strength of the neutral = 316.1(1), N1A−C1A = 135.9(2), N2A−Si1A = 166.8(1), N2A− coligand allows the isolation of molecular dinuclear potassium Si2A = 166.8(1). anilides. The molecular structure and numbering scheme of 3 are displayed in Figure 2. The central structural fragment is the coordination polymer. Instead, two dinuclear units are centrosymmetric planar four-membered K2N2 ring with interconnected by contacts between the potassium atoms and different K−N bond lengths of 279.4(3) and 291.6(3) pm. the π systems of the aryl groups. The highly ionic nature of the The shorter K−N distance belongs to an interaction between K−N interactions leads to strong electrostatic attractions K1 and an sp2 hybrid orbital of N1, whereas the other between the nitrogen atom and the silicon atoms and, hence, potassium shows a more side-on coordination to the anilide short Si−N2 bonds of 166.8(1) pm due to back-donation of anion (pz orbital at N1), leading also to rather short contacts to charge from the nitrogen atom to the silyl groups (hyper- C1 (314.8(3) pm) and C6 (329.3(3) pm). The nonbonding conjugation into σ*(Si−C) bonds). The short N2−Si bonds trans-annular K1···K1A contact adopts a rather large value of enforce a large Si1−N2−Si2 bond angle of 133.43(8)° due to 421.1(1) pm. The coordination sphere of potassium is repulsive forces between the bulky trimethylsilyl groups. A saturated by nitrogen bases of the pmdeta ligand, which similar effect was already discussed for dimeric [KN- − 21 shows two short K N bonds (289.2(3) and 296.9(3) pm) and (SiMe3)2]2. one significantly larger K−N distance of 318.3(3) pm. Crystalline monomeric 2,6-diisopropylanilides of calcium The central four-membered K2N2 ring is also formed for were obtained with multidentate coligands such as pmdeta and μ μ heteroleptic [(dme)K{ -N(SiMe3)2}{ -N(H)Dipp}K]2 (4), dme, yielding [(pmdeta)Ca{N(H)Dipp}2](7) and [(dme)2Ca- which is shown in Figure 3. The bulky bridging bis- {N(H)Dipp}2](8), respectively. The molecular structure and (trimethylsilyl)amide anions together with bidentate 1,2- numbering scheme of 7 is displayed in Figure 4. The dimethoxyethane hinder the formation of a one-dimensional pentacoordinate calcium atom binds to two anilide anions

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to complex 7. The N−Ca−N angles for the molecules A−D vary significantly and are larger for A, B, and D despite a larger coordination number (molecule A, 115.2(2)°; molecule B, 117.6(1)°; molecule C, 88.6(1)°; molecule D, 122.3(1)°), whereas molecule C deviates from the other molecules and a very small value is observed. Intramolecular strain leads to strongly widened Ca−N−C angles, and the four molecules show different values (molecule A, 156.8(3) and 157.0(3)°; molecule B, 137.0(3) and 154,6(3)°; molecule C, 147.5(3) and 149.6(3)°; molecule D, 159.2(3) and 137.4(3)°). The flexibility of the Ca−N−C angles supports the chemical intuition that electrostatic and steric forces dominate the structure and that covalent Ca−N bond contributions play insignificant roles. In heterobimetallic amides the less electropositive metal commonly binds to the amido ligands, forming a metalate, Figure 4. Molecular structure and numbering scheme of 7. The whereas the more electropositive metal represents the counter- ellipsoids represent a probability of 40%, and H atoms are not drawn. cation. We included the heterobimetallic amide with a − − Selected bond lengths (pm): Ca1 N1 = 232.4(4), Ca1 N2 = potassium to calcium ratio of 2:1 in our structural investigations 229.2(5), Ca1−N3 = 259.5(5), Ca1−N4 = 258.0(5), Ca1−N5 = ff − − because mixed-metal amides often behave di erently than the 255.2(5), N1 C1 = 137.5(6), N2 C13 = 137.0(6). Selected bond homometallic congeners.13,14 The K to Ca ratio of 2:1 justifies angles (deg): N1−Ca1−N2 = 112.9(2), Ca1−N1−C1 = 136.7(3), Ca1−N2−C13 = 146.1(4). considering this derivative as a higher order calciate. Therefore, the structure of the calciate [K2Ca{N(H)Dipp}4]∞ (9) was determined and a section of the coordination polymer is and a tridentate pmdeta ligand. Due to additional electrostatic displayed in Figure 6. The calcium atom is in a distorted- attraction the Ca1−N1 and Ca1−N2 distances to the anilides are more than 20 pm smaller than those to the pmdeta base. In addition, the small bite of the nitrogen bases of the pmdeta ligand (N···N distances) leads to very small N3−Ca1−N4 and N4−Ca1−N5 bond angles of 70.4(2) and 72.3(2)°. A rather small N1−Ca1−N2 bond angle of 112.9(2)° is enabled because the Ca1−N−C angles of the anilide ligands are widened to 136.7(3)° for N1 and 146.1(4)° for N2. The complex [(dme)2Ca{N(H)Dipp}2](8) crystallizes in the centrosymmetric triclinic space group with four molecules A−D in the asymmetric unit. The molecular structure and numbering scheme of molecule A is represented in Figure 5. The hexacoordinate calcium atom is located in a significantly distorted octahedral environment due to small bites of the dme Figure 6. Section of the polymeric structure of 9. The ellipsoids ligands and widened N−Ca−N angles. The larger coordination − represent a probability of 40%, and H atoms are neglected for clarity . number of 6 leads to lengthened Ca N bonds in comparison The letters A (−x, y, −z + 0.5) and B (−x, −y +2,−z) characterize symmetry-related atoms. Selected bond lengths (pm): Ca1−N1 = 232.9(3), Ca1−N2 = 239.3(3), K1−N1 = 294.1(3), K1−C1 = 292.9(3), K1−N2 = 287.2(3), K1−C13B = 335.0(3), K1−C14B = 324.1(3), K1−C15B = 308.8(3), K1−C16B = 304.2(4), K1−C17B = 312.1(3), K1−C18B = 327.4(3), N1−C1 = 137.9(4), N2−C13 = 137.9(4). Selected bond angles (deg): N1−Ca1−N2 = 100.3(1), N1− Ca1−N1A = 152.4(2), N1−Ca1−N2A = 98.6(1), N2−Ca1−N2A = 93.2(1), Ca1−N1−C1 = 155.8(3), Ca1−N1−K1 = 90.5(1), Ca1− N2−C13 = 127.0(2), Ca1−N2−K1 = 90.93(9).

tetrahedral environment with N−Ca−N angles between 93.2(1) and 153.4(2)°. Despite the small coordination number of 4, rather large Ca−N bond lengths of 232.9(3) and 239.3(3) pm are observed due to electrostatic repulsion between the amide anions and intramolecular steric strain between the bulky Figure 5. Molecular structure and numbering scheme of 8. The aryl groups of neighboring amido ligands. The flexibility of the ellipsoids represent a probability of 40%, and H atoms are omitted for − − ° − Ca N C bond angles (155.8(3) and 127.0(2) )again clarity reasons. The asymmetric unit contains four molecules A D; supports the mainly ionic nature of this compound. These only molecule A is depicted. Selected bond lengths (pm): Ca1A−N1A − − − tetrakis(anilido)calciates are interconnected by potassium = 230.6(4), Ca1A N2A = 231.6(4), Ca1A O1A = 242.5(3), Ca1A − O2A = 249.6(4), Ca1A−O3A = 242.8(3), Ca1A−O4A = 249.7(3), countercations that bind to the nitrogen atoms (K N= N1A−C1A = 136.9(5), N2A−C13A = 138.0(5). Selected bond angles 287.2(3) and 294.1(3) pm) and saturate their coordination (deg): N1A−Ca1A−N2A = 115.2(2), Ca1A−N1A−C1A = 156.8(3), sphere by Lewis acid−base interactions to the π systems of the Ca1A−N2A−C13A = 157.0(3). aryl groups. The remarkable reactivity can be understood on

2652 dx.doi.org/10.1021/om4001007 | Organometallics 2013, 32, 2649−2660 Organometallics Article

a Table 1. Average Bond Lengths (pm) of Selected Amides of Potassium and Calcium as Well as Their Mixed-Metal Derivatives

compd av Ca−NavK−NavCa−LavK−L ref Potassium Amides

[KN(SiMe3)2]2 278.7 21

[(tmeda)KTmp]2 279.2 295.1 (N) 22

[(thf)3KNPh2]2 282.6 272.0 (O) 23

[(pmdeta)KNPh2]2 282.9 292.2 (N) 24

[(pmdeta)KN(iPr)Ph]2 289.1 297.7 (N) 24

[(dme)2KN(iPr)Ph]2 287.3 286.8 (O) 24

[(pmdeta)KN(H)Dipp]2 285.5 301.5 (N) this work

[(diox)1.5KNPh2]∞ 284.6 270.7 (O) 25

[(tmeda)1.5KNPh2]∞ 287.4 290.5 (N) 26

[{KN(Me)Ph}3]∞ 282.4 24

[{(thf)0.5KN(iPr)Ph}2]∞ 279.7 276.3 (O) 24

[{(thf)KN(iPr)Ph}5]∞ 280.8 272.9 (O) 24

[(dme)0.25KN(iPr)Ph]∞ 281.0 278.1 (O) 24 [(thf)KN(H)Dipp]∞ 276.4 290.7 (O) this work Calcium Amides

[(thf)2Ca{N(SiMe3)2}2] 230.2 237.7 (O) 27

[(dme)Ca{N(SiMe3)2}2] 227.1 239.7 (O) 28

[(tmeda)Ca{N(SiMe3)2}2] 231.5 259.2 (N) 10

[(tmeda)Ca(Tmp)2] 227.5 264.5 (N) 9

[(tmeda)Ca{N(iPr)2}2] 227.2 260.2 (N) 10

[(dme)2Ca(NPh2)2] 236.9 246.1 (O) 8

[(thf)4Ca{N(Me)Ph}2] 241.5 240.7 (O) 12

[(thf)3Ca{N(iPr)Ph}2] 234.9 242.7 (O) 9

[(thf)2Ca{N(SiMe3)Dipp}2] 232.6 235.6 (O) 7c

[(thf)2Ca{N(SiMe3)Mes}2] 230.4 234.3 (O) 7b

[(tmeda)Ca{N(SiMe3)Mes}2] 231.1 252.9 (N) 7b

[(dme)2Ca{N(H)Dipp}2] 231.1 246.2 (O) this work

[(pmdeta)Ca{N(H)Dipp}2] 230.8 257.6 (N) this work Potassium Calciates

[(thf)4K2Ca{N(iPr)Ph}4] 241.8 268.7 9

[(tmeda)2K2Ca{N(iPr)Ph}4] 244.1 294.6 283.7 15

[(thf)3K2Ca(NPh2)4]∞ 240.3 265.2 9

[K2Ca{N(H)Dipp}4]∞ 236.1 290.7 Tthis work aAbbreviations: diox, 1,4-dioxane; Dipp, 2,6-diisopropylphenyl; dme, 1,2-dimethoxyethane; L, neutral Lewis base such as ethers and amines; Me, methyl; Mes, 2,4,6-trimethylphenyl; Ph, phenyl; pmdeta, pentamethyldiethylenetriamine; Pr, propyl; thf, tetrahydrofuran; tmeda, tetramethylethylenediamine; Tmp, 2,2,6,6-tetramethylpiperidide. the basis of a small coordination number of calcium at benzyl alkali-metal solvates;29 whereas lithium and sodium (accessibility of calcium by the substrate) and of electrostatic ions show the shortest distances to the methylene unit, the repulsion between the anilide anions (enhancing the nucleo- potassium ion prefers a side-on coordination to the aromatic π philicity and availability of the anilide anions) in addition to system of the phenyl group. This finding supports the notion increased nucleophilicity caused by the electron-donating that the potassium ion represents a significantly softer cation isopropyl groups. than the lighter congeners and the doubly charged calcium ions. Selected structural parameters of potassium and calcium In heterobimetallic amides of potassium and calcium, the amido amides are compared in Table 1. The amides of the heavier anions always bind to the harder divalent calcium ion, forming alkali metals and alkaline-earth metals have attracted tremen- tetrakis(amido)calciates with tetracoordinate calcium centers. dous interest because they react as highly reactive nucleophiles Due to the concentration of negative charge in the vicinity of and metalation reagents as well as hydroamination catalysts.17 calcium, neutral Lewis bases such as thf and tmeda bind at The reactivity can be adjusted with the s-block metals potassium. If the neutral coligands have weak coordination potassium and calcium or even by employing their hetero- properties toward K+ ions in comparison to the π systems of bimetallic derivatives. Due to a larger size of the potassium ion the phenyl groups, interactions between the potassium ion and and its smaller charge, the Ca−N bonds are generally the π systems of aryl substituents are operative, often leading to significantly shorter than the K−N bonds. Small variations aggregation and formation of coordination polymers. depend on the coordination number of the s-block metals and Hydroamination of Diphenylbutadiyne. Hydroamina- on the bulkiness of the amides and coligands. In solvent- tion is an atom-economic process for the preparation of depleted compounds, the potassium ions also form strong substituted amines. However, thermodynamic and kinetic bonds to the π systems of aryl groups, whereas solvent-free challenges aggravate the direct nucleophilic attack of the calcium amides dimerize via bridging amido ligands.28 This π- amine at an electron-rich C−C multiple bond. In addition, the philicity of the potassium ion was already investigated in detail large energy difference between the N−H and the C−C

2653 dx.doi.org/10.1021/om4001007 | Organometallics 2013, 32, 2649−2660 Organometallics Article multiple bond and entropic effects are disadvantageous. Scheme 3. Calciate-Mediated Hydroamination of Therefore, activation of the C−C multiple bond (by side-on Diphenylbutadiyne with 2,6-Diisopropylaniline in a coordination to transition metals) or of the amine (amide or Tetrahydrofuran, Yielding Tetracyclic Imine 10 imide formation at electropositive metals and lanthanoids) is required. Intermolecular hydroamination of diphenylbutadiyne with diphenylamine required a very reactive catalyst.16,20 Whereas the reactivity of the diphenylamides of potassium and calcium were insufficient to mediate this hydroamination reaction, catalytic amounts of heterobimetallic [K2Ca(NPh2)4] led to the formation of singly hydroaminated diphenylbutadiyne.16 In contrast to this finding, the more nucleophilic N-isopropylani- lides of potassium and of calcium are able to mediate the hydroamination of diphenylbutadiyne with N-isopropylaniline. aSee text and Figure 7. The potassium-mediated hydroamination of diphenylbutadiyne with N-isopropylaniline gave small amounts of the side product 1-isopropylphenylamino-2,4-bis(phenylethynyl)-3-phenylnaph- thalene with a 2:1 stoichiometry of diphenylbutadiyne to aniline.16 Hydroamination of butadiynes yielding pyrroles succeeds via a copper(I)-catalyzed addition of aniline to diphenylbutadiyne (Scheme 2).30 Another strategy for the synthesis of pyrroles

Scheme 2. Copper(I)-Mediated Synthesis of Pyrroles via Double Hydroamination of Diphenylbutadiyne with Aniline

Figure 7. Ball-and-stick model of 2,6-diisopropyl-9,11,14,15-tetra- phenyl-8-azatetracyclo[8.5.0.01,7.02,13]pentadeca-3,5,7,9,11,14-hexaene (10), clarifying the building blocks of this tetracyclic compound (black and blue, C and N of 2,6-diisopropylaniline; yellow and green, two was developed via the titanium-mediated double hydro- diphenylbutadiyne units). The H atoms (light gray) are neglected, amination of 1,4-pentadiynes with primary amines.31 If with the exception of those stemming from the aniline. benzylamine was used in these catalytic hydroamination − reactions, pyridine derivatives were obtained.30 32 Here we The molecular structure of 10 is displayed in Figure 8. The investigated the calcium-mediated hydroamination of diphe- labeling of the atoms shows the numbering in accordance with nylbutadiyne with 2,6-diisopropylaniline. A single hydro- the chemical name for the inner tetracyclic unit, with the amination would yield 1,4-diphenyl-1-(2,6-diisopropylanilino)- nitrogen atom N8 being in position 8. For the numbering of but-1-ene-3-yne, and a second intramolecular hydroamination the substituents, the digit of the adjacent ring atom was step could allow the isolation of N-2,6-diisopropylphenylpyr- expanded by an additional digit to distinguish the carbon atoms role. However, the hydroamination of diphenylbutadiyne with within a substituent. primary 2,6-diisopropylaniline proceeded surprisingly different The nitrogen atom N8 is bound in a five-membered ring with in the presence of catalytic amounts of 9. Similarly to the aC7N8 double bond and a N8−C9 single bond of 131.2(2) observation of the formation of the naphthalene side product,16 and 141.8(2) pm, respectively. From these values it is obvious 1 equiv of aniline reacted with 2 equiv of butadiyne, as shown that there is no significant delocalization within the conjugated in Scheme 3, regardless of the applied stoichiometry. In Figure system. A vast steric strain is introduced at the C1 atom, which 7 the color code clarifies the origin of the building blocks (black is a member of all four cycles. This fact leads to severe and blue, C and N of 2,6-diisopropylaniline; yellow and green, deviations from a tetrahedral environment (C−C1−C values two diphenylbutadiyne units). This compound cocrystallized deviate from 101.2(1) to 120.3(2)°) toward a trigonal- with half a diphenylbutadiyne molecule. pyramidal environment33 and to a significant elongation of The resulting crystalline tetracyclic imine, 2,6-diisopropyl- the C1−C bonds. The adjacent C2 atom even shows stronger 9,11,14,15-tetraphenyl-8-azatetracyclo[8.5.0.01,7.02,13]- deviations from ideal tetrahedral symmetry. The smallest C1− pentadeca-3,5,7,9,11,14-hexaene (10), was obtained with a yield C2−C13 angle shows a value of only 95.7(1)° between three of 82%. The formation of this product does not depend on the sp3-hybridized carbon atoms and a C2−C13 bond length of reaction temperature and succeeded in boiling THF and at 157.5(2) pm. Distortions also widen the angles at the vicinal ambient temperature; only the reaction period was extended at diphenylethene fragment with C15−C14−C141 and C14− lower temperatures. C15−C151 values of 129.9(2) and 130.1(2)°, respectively.

2654 dx.doi.org/10.1021/om4001007 | Organometallics 2013, 32, 2649−2660 Organometallics Article

thermally controlled Bergman cyclization reactions of non- conjugated (Z)-hexa-1,5-diyne-3-ene yields p-benzyne with a triplet ground state,37 whereas photochemically induced cyclizations follow other pathways.38 The Bergman cyclization can be triggered by heat39 and by internal amide function- alities,40 occasionally also metal-mediated.41 A final rearrangement step yields tetracyclic 2,6-diisopropyl- 9,11,14,15-tetraphenyl-8-azatetracyclo[8.5.0.01,7.02,13]- pentadeca-3,5,7,9,11,14-hexaene (10; 5a,9-diisopropyl- 2,3,10,11-tetraphenyl-5,5a-dihydro-2a1,5-ethenocyclohepta[cd]- isoindole), containing three chiral carbon atoms at positions 1, 2, and 13. The driving force of this final reorganization of the molecule, which divides the π system into a shorter conjugated unit (C3−C12) and an isolated C14C15 double bond, is Figure 8. Molecular structure and numbering scheme of 10. The release of steric strain between the isopropyl group at C2 and ellipsoids represent a probability of 40%, and all H atoms are omitted the phenyl group at C15 (which are oriented to opposite sides for clarity. Selected bond lengths (pm): C1−C2 = 156.2(2), C1−C7 = of molecule 10) as well as between neighboring phenyl 150.2(2), C1−C10 = 151.6(2), C1−C15 = 154.8(2), C2−C3 = substituents. Due to the strained tetracyclic structure only two 150.4(3), C2−C21 = 155.2(3), C3−C4 = 134.1(3), C4−C5 = − − − enantiomers were observed and characterized by X-ray 145.7(3), C5 C6 = 135.2(3), C6 C7 = 144.4(3), C6 C61 = crystallography and NMR studies in order to verify the 152.4(3), C7−N8 = 131.2(2), N8−C9 = 141.8(2), C9−C10 = 136.6(3), C9−C91 = 147.9(3), C10−C11 = 145.0(2), C11−C12 = proposed structure. − − − During extensive NMR investigations of 10 it was observed 135.5(3), C11 C111 = 149.0(3), C12 C13 = 151.1(3), C13 C14 = fi 153.3(3), C14−C15 = 134.2(3), C14−C141 = 147.5(2), C15−C151 that new resonances developed within a few days that nally = 147.7(3). grew to an approximate equimolar ratio with starting 7,15- diisopropyl-2,3,10,12-tetraphenyl-9-azatetracyclo- [8.5.0.01,7.02,13]pentadeca-3,5,7,9,11,14-hexaene (10). A com- Initially it was astonishing that tetracyclic imine 10 with three plete conversion to 5a,9-diisopropyl-2,3,10,11-tetraphenyl-5a,6- chiral carbon atoms formed in such a selective manner. The dihydro-2a1,6-ethenocyclohepta[cd]isoindole (11)andalso proposed reaction mechanism is presented in Scheme 4, fi ff ff fi puri cation e orts have failed as of yet. Therefore, the structure o ering two feasible pathways. The rst reaction step is the of the rearrangement product 11 was derived from NMR addition of an anilide to the triple bond of diphenylbutadiyne, spectra and DFT calculations. A rearrangement mechanism is yielding A. Another alkyne inserts into the newly formed proposed in Scheme 5. This rearrangement breaks and forms a metal−carbon bond (carbometalation step to B). Thereafter, an − π − C C bond and rearranges the conjugated system; however, intramolecular metalation yields amide C with a metal the number and size of rings as well as double bonds remain nitrogen bond. The very nucleophilic amido base forms an unchanged in the resulting 11, suggesting solely reduction of imine, and cyclization leads to the formation of the 1,2,4,6- intramolecular strain as the driving force for this rearrangement. cycloheptratetraene derivative D with the negative charge at the Consequently the energy difference between 10 and 11 is 5-position (exemplified in Scheme 4 by an M−C bond). This − rather small, with 11 being favored by 17.46 kJ mol 1 according carbanion reacts with H N-Dipp, thus regenerating the 2,6- 2 to DFT calculations. A comparison of experimental and diisopropylanilido catalyst M{N(H)Dipp} and leading to calculated NMR data (Table 2; for assignments see Scheme intermediate metal-free E. The 1,2,4,6-cycloheptratetraene fi fragment is very reactive, due to ring strain caused by the 6) shows slightly low eld shifted resonances. Nevertheless, ketene moiety. Therefore, a cyclization reaction releases this experimental parameters are in accordance with the calculated values. The trends are expressed correctly, clearly supporting strain and annihilates the aromatic character of the Dipp group, fi resulting in the tricyclic derivative F. Strained 1,2,4,6-cyclo- the above suggested interpretation of the experimental ndings. heptatetraenes have already attracted much interest and were In order to support the proposed reaction mechanisms and 34 to deduce the importance of steric strain for the rearrangement prepared and preserved in an argon matrix. Isomeric C(CH)6 was intensively investigated by quantum chemical methods as step from F to 10 and from 10 to 11, quantum chemical free molecules35 as well as a hydrocarbon captured in a investigations were performed. molecular container.36 These investigations show that 1,2,4,6- Quantum Chemical Investigations. Total energies Ecorr cycloheptatetraene is favored in comparison to a carbene with thermal and entropic corrections being applied as well as embedded in a seven-membered ring. the number of imaginary frequencies are summarized in Table fi An alternative pathway allows the protonation of C (and, 3. We started our investigations on a simpli ed unsubstituted hence, the formation of amine G, which is shown here with a model (marked with “_H”; Scheme 4, R = R′ = H). Here −1 collinear arrangement of the alkyne units requiring a specific derivative F_H is favored by 64.5 kJ mol in comparison to the  1,2,4,6-cycloheptatetraene intermediate E_H. Surprisingly, the isomerism at the C C double bonds) combined with the re- − formation of the anilido catalyst (Scheme 4). Thereafter, a derivative F_H also is 60.5 kJ mol 1 lower in energy than 10_H Bergman cyclization leads to the formation of the diradical without isopropyl and phenyl groups. Due to the fact that − species H, which also rearranges to the tricyclic imine F, unsubstituted 11_H is only 17.4 kJ mol 1 lower in energy than accompanied by a hydrogen abstraction from the amino 10_H, derivative F_H represents the thermodynamically most functionality. This hydrogen transfer from the amino unit to stable product: i.e., in theory the calciate-mediated reaction of the carbon atom is accompanied by C−C bond formation, aniline with butadiyne might well end with the formation of leading to a breakup of the aromaticity of the Dipp group. The F_H.

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a Scheme 4. Proposed Mechanism for the Calciate-Mediated Formation of Imine 10

aR=iPr, R′ = Ph; see text.

Scheme 5. Rearrangement of 10, Yielding 5a,9-Diisopropyl- groups. Optimization of F_S leads to the highly endothermic 2,3,10,11-tetraphenyl-5a,6-dihydro-2a1,6- formation of an intermediate in which the neighboring phenyl ethenocyclohepta[cd]isoindole (11) substituents performed a formal [2 + 2] cycloaddition reaction, which is not a productive reaction pathway in the context of the experimentally observed reaction. Therefore, F_S cannot be considered as an intermediate in the formation of tetracyclic 10_S and 11_S but might be considered as a transition state. Moreover, the substituted intermediate E_S is energetically favored by 13.3 kJ mol−1 in comparison to 10_S and is only 4.3 kJ mol−1 less stable than substituted 11_S. The latter nevertheless is the thermodynamically most stable isomer if Taking the substituents into account (designated with “_S”; the substituted derivatives are considered. The alternative ′ fi fi pathway via intermediate G_S is feasible from a theoretical R=iPr, R = Ph), the situation changes signi cantly. In the nal −1 rearrangement from 10_S to 11_S the situation is similar to point of view because substituted G_S is 48.2 kJ mol higher that for the unsubstituted derivatives, with product 11_S again in energy than 10_S. In summary, the substitution pattern being favored by 17.6 kJ mol−1. However, the substituted dramatically disadvantages intermediate F_S, although the molecule F_S does not represent a minimum structure, due to unsubstituted derivative F_H represents the favored molecule if massive intramolecular strain between neighboring phenyl phenyl and isopropyl groups are neglected. Hence, the reaction

2656 dx.doi.org/10.1021/om4001007 | Organometallics 2013, 32, 2649−2660 Organometallics Article

Table 2. Comparison of Experimental and Calculated is pushed toward the tetracycle 10_S in order to reduce 13C{1H} NMR Shifts of the Central Tetracyclic Units of 10 intramolecular repulsion between adjacent phenyl groups. a and 11 ■ CONCLUSION 10 11 Metalation of 2,6-diisopropylaniline with K[N(SiMe3)2] yields exptl DFT exptl DFT the corresponding potassium salt [K{N(H)Dipp}·KN- 181.0 185 170.0 174 (SiMe3)2](1), regardless of the applied stoichiometry. At 146.2 156 160.4 168 elevated temperatures homoleptic K{N(H)Dipp} (5) can be 140.3 153 137.7 145 isolated. The aggregation degree of these potassium anilides 139.2 146 136.4 144 strongly depends on the denticity of the neutral coligand. The 138.9 145 135.9 142 μ addition of monobasic THF leads to polymeric [( -thf)K2{N- 136.2 145 133.9 142 (H)Dipp}2]∞ (2) in the solid state. Bidentate DME is able to 135.6 144 131.7 141 μ μ stabilize tetranuclear [(dme)K{ -N(SiMe3)2}{ -N(H)Dipp}- 131.6 140 131.3 141 K]2 (4), whereas in the presence of tridentate PMDETA 127.5 134 127.4 138 dinuclear [(pmdeta)K{N(H)Dipp}]2 (3) crystallizes. In all 126.8 134 127.2 138 these solids the four-membered K2N2 ring is the dominating 125.5 130 126.9 133 structural unit which can be interconnected via Lewis acid− 77.8 83 66.5 72 base interactions between the soft potassium cations and the 72.8 82 57.7 64 aryl π-systems. 58.3 67 48.6 58 These potassium anilides can be used as anilide transfer a The assignment of the chemical shifts is depicted in Scheme 6. reagents. Thus, the metathetical approach with CaI2 in tetrahydrofuran yields the corresponding calcium bis(2,6- 1 δ 13 Scheme 6. Calculated H (Chemical Shifts , left) and C diisopropylanilide) [(thf)nCa{N(H)Dipp}2](6), which can be NMR Data (Right) of 10 (Top Row) and 11 (Bottom Row) purified and crystallized as monomeric and mononuclear complexes after addition of tri- and bidentate coligands such as pmdeta or dme, yielding [(pmdeta)Ca{N(H)Dipp}2](7) and [(dme)2Ca{N(H)Dipp}2](8), respectively. Excess potas- sium 2,6-diisopropylphenylamide leads to the formation of the calciate [K2Ca{N(H)Dipp}4]∞ (9). The potassium tetrakis(anilido)calciate 9 is highly reactive and enables a calciate-mediated hydroamination of diphenylbu- tadiyne with 2,6-diisopropylaniline. However, after this reaction step and a subsequent carbometalation of another butadiyne a reaction cascade leads to the formation of tetracyclic 2,6- diisopropyl-9,11,14,15-tetraphenyl-8-azatetracyclo- [8.5.0.01,7.02,13]pentadeca-3,5,7,9,11,14-hexaene (10), which slowly rearranges to 5a,9-diisopropyl-2,3,10,11-tetraphenyl- 5a,6-dihydro-2a1,6-ethenocyclohepta[cd]isoindole (11). ■ EXPERIMENTAL SECTION General Remarks. All manipulations were carried out under an argon or a nitrogen gas atmosphere using standard Schlenk techniques. Solvents were dried according to common procedures and distilled under argon or nitrogen; deuterated solvents were dried with sodium, degassed, and saturated with an inert gas. KN(SiMe3)2 was purchased from Aldrich as a solid with a purity of 95% and used without further purification. Bruker AC 200, Bruker AC 400, and Bruker AC 600 spectrometers were used to record 1H NMR and 13C NMR spectra at Table 3. Calculated Energies and Numbers of Imaginary ambient temperature in [D8]THF solutions if no other solvent is Frequencies mentioned. All spectra were referenced to deuterated THF as an compda E (au) N internal standard. The anilido complexes were extremely sensitive corr Imag toward moisture and air, and therefore, combustion analysis gave no − E_H 594.722615 0 reliable results. E_S −1754.647508 0 Synthesis of K{N(H)Dipp}K{N(SiMe3)2} (1). KN(SiMe3)2 (2.15 g, F_H −594.747172 0 10.8 mmol) was dissolved in 22 mL of toluene and the solution filtered − G_H 594.695420 0 prior to use. To this clear, colorless solution was added H2N-Dipp (1.0 G_S −1754.624103 0 mL, 5.3 mmol) via syringe with vigorous stirring at room temperature 10_H −594.724130 0 to yield a colorless precipitate of 1. After 3 h of stirring, pure 1 was fi fi 10_S −1754.642443 0 isolated by ltration, washed twice with 7.5 mL of toluene and nally − with 10 mL of pentane, and then dried in vacuo. Yield: 2.05 g (4.9 11_H 594.730775 0 1 δ 3 mmol, 93%). H NMR: 6.89 (2H, d, JH,H = 7.4 Hz, m-H), 5.84 (1H, 11_S −1754.649164 0 3 3 t, JH,H = 7.4 Hz, p-H), 3.41 (1H, s, NH), 3.12 (2H, hept, JH,H = 6.8 a “ ” ′ 3 − For all compounds denoted with the ending _H ,R=R = H; for all Hz, CH), 1.16 (12H, d, JH,H = 6.8 Hz, CH3), 0.19 (18H, s, SiCH3). compounds denoted with the ending “_S”,R=iPr, R′ = Ph. 13C{1H} NMR: δ 156.6 (i-C), 129.7 (o-C), 122.1 (m-C), 106.7 (p-C), 28.2 (CH), 23.1 (iPrCH3), 6.4 (SiCH3).

2657 dx.doi.org/10.1021/om4001007 | Organometallics 2013, 32, 2649−2660 Organometallics Article

μ 3 Synthesis of [( -thf)K2{N(H)Dipp}2]∞ (2). This approach was 3.96 (4H, s, NH), 3.03 (8H, hept, JH,H = 6.8 Hz, CH), 1.20 (48H, d, 3 13 1 δ performed to yield a tmeda adduct. Therefore, 1 (256 mg, 0.6 mmol) JH,H = 6.8 Hz, CH3). C{ H} NMR: 147.4 (i-C), 131.4 (o-C), 122.6 was dissolved in 1.5 mL of a 2:1 mixture of TMEDA and THF, and (m-C), 113.8 (p-C), 28.3 (CH), 23.0 (iPrCH3). this reaction mixture was heated to 60 °C. Crystalline 2 was obtained Synthesis of 2,6-Diisopropyl-9,11,14,15-tetraphenyl-8- overnight from this solution at ambient temperature. 1H NMR: δ 6.57 azatetracyclo[8.5.0.01,7.02,13]pentadeca-3,5,7,9,11,14-hexaene 3 3 (4H, d, JH,H = 7.4 Hz, m-H), 5.81 (2H, t, JH,H = 7.4 Hz, p-H), 3.62 (10). Diphenylbutadiyne (0.51 g, 2.47 mmol) was dissolved in 12 mL 3 (thf), 3.45 (2H, s, NH), 3.15 (4H, hept, JH,H = 6.8 Hz, CH), 1.78 of THF before 2,6-diisopropylaniline (0.23 mL, 1.26 mmol) and 5 mol 3 13 1 δ (thf), 1.17 (24H, d, JH,H = 6.8 Hz, CH3). C{ H} NMR: 157.2 (i- % of the calciate 9 were added, and the mixture was stirred overnight. C), 129.6 (o-C), 122.1 (m-C), 106.3 (p-C), 68.1 (thf), 28.3 (CH), 26.3 A standard workup procedure including hydrolysis with 15 mL of (thf), 23.3 (CH3). water, extraction with diethyl ether, drying with sodium sulfate, and Synthesis of [(pmdeta)K{N(H)Dipp}]2 (3). 1 (255 mg, 0.6 mmol) recrystallization from pentane gave 10 as a crude product which was dissolved in a mixture of 2 mL of PMDETA and 0.3 mL of THF, contained half a molecule of diphenylbutadiyne per formula unit. Final and this solution was heated to 60 °C. Standing at room temperature purification was performed via gradient column chromatography over 1 δ 3 yielded crystalline needles of 3. H NMR: 6.56 (4H, d, JH,H = 7.4 silica gel, starting with pure aliphatic hydrocarbons followed by a 1:1 3 Hz, m-H), 5.78 (2H, t, JH,H = 7.4 Hz, p-H), 3.39 (2H, s, NH), 3.15 mixture of alkanes and ethyl acetate. The residue was recrystallized 3 − − ° (4H, hept, JH,H = 6.8 Hz, CH), 2.29 2.44 (CH2-pmdeta), 2.19 + 2.15 from pentane at 20 C, yielding orange 10 (0.60 g, 1.03 mmol, 82%). 3 13 1 δ − ° (CH3-pmdeta), 1.16 (24H, d, JH,H = 6.8 Hz, CH3). C{ H} NMR: Mp: 122 125 C. NMR data without phenyl groups are as follows 1 δ 157.9 (i-C), 129.5 (o-C), 122.1 (m-C), 105.8 (p-C), 58.8 + 57.3 (CH2- (for assignment see Scheme 6). H NMR (C6D6, 600 MHz, 295 K): 3 3 pmdeta), 46.1 + 43.2 (CH3-pmdeta), 28.3 (CH), 23.3 (iPrCH3). 6.54 (1H, d, JH,H = 6.4 Hz), 6.24 (1H, dd, JH,H = 8.6 + 12.1 Hz), 6.14 μ μ 3 3 Synthesis of [(dme)K{ -N(SiMe3)2}{ -N(H)Dipp}K]2 (4). 1 (316 (1H, d, JH,H = 8.6 Hz), 5.81 (1H, d, JH,H = 12.1 Hz), 3.96 (1H, d, 3 3 mg, 0.8 mmol) was dissolved in 1 mL of DME. Subsequent cooling to JH,H = 6.4 Hz), 3.62 (1H, hept, JH,H = 6.9 Hz, CH-iPr), 1.89 (1H, ° 1 3 3 5 C for about 1 week quantitatively resulted in crystalline 4. H hept, JH,H = 6.9 Hz, CH-iPr), 1.18 (3H, d, JH,H = 6.9 Hz, CH3-iPr), δ 3 3 3 3 NMR: 6.58 (4H, d, JH,H = 7.4 Hz, m-H), 5.83 (2H, t, JH,H = 7.4 Hz, 0.81 (3H, d, JH,H = 7.0 Hz, CH3-iPr), 0.80 (3H, d, JH,H = 7.0 Hz, 3 13 1 p-H), 3.43 (2H, s, NH), 3.43 (CH2-dme), 3.27 (CH3-dme), 3.12 (4H, CH3-iPr), 0.52 (3H, d, JH,H = 6.8 Hz, CH3-iPr). C{ H} NMR 3 3 − δ hept, JH,H = 6.8 Hz, CH), 1.16 (24H, d, JH,H = 6.8 Hz, CH3), 0.19 (C6D6, 150 MHz, 295 K): 181.0, 146.2, 140.3, 139.2, 138.9, 136.2, 13 1 δ (36H, s, SiCH3). C{ H} NMR: 156.7 (i-C), 129.7 (o-C), 122.1 (m- 135.6, 131.6, 127.5, 126.8, 125.5, 77.8, 72.8, 58.3, 30.8, 30.8, 23.1, 22.3, C), 106.7 (p-C), 72.6 (CH2-dme), 58.8 (CH3-dme), 28.3 (CH), 23.2 18.7, 17.7. Anal. Calcd for C44H39N (581.78): C, 90.84; H, 6.76; N, (iPrCH3), 6.5 (SiCH3). 2.41. Found: C, 90.80; H, 6.90; N, 2.40. MS (EI, m/z (%)): 581 (12) + − + Synthesis of K{N(H)Dipp} (5). H2N-Dipp (0.98 mL, 5.2 mmol) [M] , 379 (40) [M diyne] , 202 (44) [diyne], 177 (100) + + was added via syringe to a clear colorless solution of KN(SiMe3)2 [C12H19N] , 162 (68) [C12H17] . IR: 1599 w, 1491 w, 1443 w, (1.033 g, 5.2 mmol) in 15 mL of toluene. The resulting suspension 1261 m, 1177 w, 1056 w, 1027 m, 964 w, 917 w, 839 m, 756 s, 693 vs, was heated to 100 °C for 18 h, yielding an off-white powder of 5 that 662 w, 608 w, 531 w, 417 w cm−1. contains only trace amounts of the initial amide. Yield: 1.02 g (4.7 Synthesis of 5a,9-Diisopropyl-2,3,10,11-tetraphenyl-5a,6- 1 δ 3 1 cd mmol, 91%). H NMR: 6.55 (2H, d, JH,H = 7.4 Hz, m-H), 5.75 (1H, dihydro-2a ,6-ethenocyclohepta[ ]isoindole (11). In solution 3 3 t, JH,H = 7.4 Hz, p-H), 3.36 (1H, s, NH), 3.16 (2H, hept, JH,H = 6.8 product 10 rearranged with reduction of intramolecular steric strain, 3 − ∼ Hz, CH), 1.16 (12H, d, JH,H = 6.8 Hz, CH3), 0.19 (1.2 H-equ, 7% yielding 11. Due to the fact that this compound always contained 13 1 δ fi SiCH3). C{ H} NMR: 157.6 (i-C), 129.5 (o-C), 122.1 (m-C), signi cant amounts of 10, characterization was limited to NMR data. 105.5 (p-C), 28.3 (CH), 23.3 (iPrCH3), 6.5 (SiCH3). NMR parameters without phenyl groups are as follows (for 1 δ Synthesis of [(thf)xCa{N(H)Dipp}2] (6). 5 (1.10 g, 5.1 mmol) and assignment see Scheme 6). H NMR (C6D6, 600 MHz, 295 K): 3 3 CaI2 (0.75 g, 2.5 mmol) were dissolved in 15 mL of THF. 6.58 (1H, d, JH,H = 12.2 Hz), 6.53 (1H, d, JH,H = 9.5 Hz), 6.49 (1H, 3 3 Immediately, a white precipitate of KI formed that was separated by dd, JH,H = 7.6 + 12.2 Hz), 6.00 (1H, d, JH,H = 9.5 Hz), 4.64 (1H, fi 3 3 ltration over Celite after 2 h of stirring at room temperature. We note hept, JH,H = 7.0 Hz, CH-iPr), 3.91 (1H, d, JH,H = 7.5 Hz), 2.03 (1H, 3 3 that no crystalline material could be obtained from this solution. hept, JH,H = 6.9 Hz, CH-iPr), 1.33 (3H, d, JH,H = 7.0 Hz, CH3-iPr), 3 3 Instead, 6 separated as an oil from diverse solvent mixtures (THF, 1.28 (3H, d, JH,H = 7.0 Hz, CH3-iPr), 0.86 (3H, d, JH,H = 7.1 Hz, 3 13 1 toluene, hexane) during cooling. CH3-iPr), 0.73 (3H, d, JH,H = 6.8 Hz, CH3-iPr). C{ H} NMR δ Synthesis of [(pmdeta)Ca{N(H)Dipp}2] (7). A 3 mL portion of a (C6D6, 150 MHz, 295 K): 170.0, 160.4, 137.7, 136.4, 135.9, 133.9, THF solution of 6 was dried in vacuo. Redissolving in 5 mL of 131.7, 131.3, 127.4, 127.2, 126.9, 66.5, 57.7, 48.6, 29.9, 29.6, 22.6, 22.6, PMDETA and 1.75 mL of THF with heating followed by cooling to 18.2, 17.5. −20 °C overnight yielded colorless crystalline material. 1H NMR: δ Structure Determinations. The intensity data for the compounds 3 3 ff 6.63 (4H, d, JH,H = 7.4 Hz, m-H), 5.96 (2H, t, JH,H = 7.4 Hz, p-H), were collected on a Nonius KappaCCD di ractometer using graphite- 3 − α 3.31 (2H, s, NH), 3.00 (4H, hept, JH,H = 6.8 Hz, CH), 2.29 2.48 monochromated Mo K radiation. Data were corrected for Lorentz 3 ff ff 42,43 (CH2-pmdeta), 2.20 + 2.16 (CH3-pmdeta), 1.22 (24H, d, JH,H = 6.8 and polarization e ects but not for absorption e ects. 13 1 δ 44 Hz, CH3). C{ H} NMR: 156.9 (i-C), 130.4 (o-C), 122.1 (m-C), The structures were solved by direct methods (SHELXS ) and fi 2 108.7 (p-C), 58.8 + 57.3 (CH2-pmdeta), 46.1 + 43.2 (CH3-pmdeta), re ned by full-matrix least-squares techniques against Fo (SHELXL- 44 29.4 (CH), 23.4 (iPrCH3). 97 ). The hydrogen atoms of compounds 2 and 10 and the hydrogen ff Synthesis of [(dme)2Ca{N(H)Dipp}2] (8). Crystalline 8 was atoms bound to the amide functionalities were located by di erence obtained when oily 6 was dissolved in a few milliliters of DME and Fourier synthesis and refined isotropically. The other hydrogen atoms cooled to −20 °C, yielding single crystals of 8. 1H NMR: δ 6.63 (4H, were included at calculated positions with fixed thermal parameters. All 3 3 fi 44 d, JH,H = 7.4 Hz, m-H), 5.96 (2H, t, JH,H = 7.4 Hz, p-H), 3.43 (CH2- nondisordered non-hydrogen atoms were re ned anisotropically. 3 fi dme), 3.31 (2H, s, NH), 3.28 (CH3-dme), 3.00 (4H, hept, JH,H = 6.8 Crystallographic data as well as structure solution and re nement 3 13 1 δ Hz, CH), 1.22 (24H, d, JH,H = 6.8 Hz, CH3). C{ H} NMR: 157.0 details are summarized in Table S1 as part of the Supporting (i-C), 130.4 (o-C), 122.1 (m-C), 108.6 (p-C), 72.6 (CH2-dme), 58.8 Information. XP (SIEMENS Analytical X-ray Instruments, Inc.) was (CH3-dme), 29.3 (CH), 23.4 (iPrCH3). used for structure representations. Synthesis of [K2Ca{N(H)Dipp}4]∞ (9). 5 (814 mg, 3.8 mmol) and Computational Methods. Full geometry optimizations (i.e., CaI2 (280 mg, 0.9 mmol) were reacted in 10 mL of THF, and without symmetry constraints) were carried out with the GAUSSIAN precipitation of finely divided KI was observed. THF-free crystalline 09 program package using throughout the hybrid Hartree−Fock-DFT − material was obtained after reduction of the original volume of the approach (B3LYP/6-311G(d,p)).45 47 Stationary points of geometry calciate solution to one-third of its original volume, addition of 3 mL optimizations were characterized to be minimum structures according of toluene, and subsequent cooling to −20 °C for 2 weeks. 1H NMR: δ to the absence of any imaginary modes by applying second-order 3 3 6.79 (8H, d, JH,H = 7.4 Hz, m-H), 6.31 (4H, t, JH,H = 7.4 Hz, p-H), derivative calculations. NMR spectra were calculated with the

2658 dx.doi.org/10.1021/om4001007 | Organometallics 2013, 32, 2649−2660 Organometallics Article continuous set of gauge transformations (CSGT) and the gauge- 1998, 176, 157−210. (d) Westerhausen, M. Trends Organomet. Chem. independent atomic orbital (GIAO) methods.48 Visualization of any 1997, 2,89−105. calculated properties was performed using the program package (5) Utke, A. R.; Sanderson, R. T. J. Org. Chem. 1964, 29, 1261−1264. GAUSSVIEW.49 (6) (a) Johns, A. M.; Chmely, S. C.; Hanusa, T. P. Inorg. Chem. 2009, 48, 1380−1384. (b) Gillett-Kunnath, M. M.; MacLellan, J. G.; Forsyth, ■ ASSOCIATED CONTENT C. M.; Andrews, P. C.; Deacon, G. B.; Ruhlandt-Senge, K. Chem. − *S Supporting Information Commun. 2008, 4490 4492. (c) Tang, Y.; Zakharov, L. N.; Kassel, W. − Tables, figures, and CIF files giving crystallographic data of the S.; Rheingold, A. L.; Kemp, R. A. Inorg. Chim. Acta 2005, 358, 2014 crystal structure determinations as well as the NMR spectra of 2022. (d) Kuhlman, R. L.; Vaartstra, B. A.; Caulton, K. G. Inorg. Synth. the metal anilides. This material is available free of charge via 1997, 31, 8. (e) Frankland, A. D.; Lappert, M. F. J. Chem. Soc., Dalton Trans. 1996, 4151−4152. (f) Boncella, J. M.; Coston, C.; Cammack, J. the Internet at http://pubs.acs.org. Crystallographic data K. Polyhedron 1991, 10, 769−770. (g) Vaartstra, B. A.; Huffman, J. C.; (excluding structure factors) have also been deposited with Streib, W. E.; Caulton, K. G. Inorg. Chem. 1991, 30, 121−125. the Cambridge Crystallographic Data Centre as supplementary (h) Westerhausen, M.; Schwarz, W. Z. Anorg. Allg. Chem. 1991, 606, publication CCDC-888141 for 2, CCDC-888142 for 3, CCDC- 177−190. (i) Westerhausen, M. Inorg. Chem. 1991, 30,96−101. 888143 for 4, CCDC-888144 for 7, CCDC-888145 for 8, (j) Cloke, F. G. N.; Hitchcock, P. B.; Lappert, M. F.; Lawless, G. A.; CCDC-888146 for 9, and CCDC-888147 for 10. Copies of the Royo, B. J. Chem. Soc., Chem. Commun. 1991, 724−726. (k) Hitchcock, data can be obtained free of charge on application to the P. B.; Lappert, M. F.; Lawless, G. A.; Royo, B. J. Chem. Soc., Chem. CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (e-mail Commun. 1990, 1141−1142. (l) Bradley, D. C.; Hursthouse, M. B.; [email protected]). Ibrahim, A. A.; Malik, K. M. A.; Motevalli, M.; Möseler, R.; Powell, H.; Runnacles, J. D.; Sullivan, A. C. Polyhedron 1990, 9, 2959−2964. ■ AUTHOR INFORMATION (7) (a) Torvisco, A.; Ruhlandt-Senge, K. Organometallics 2011, 30, − Corresponding Author 986 991. (b) Gillett-Kunnath, M.; Teng, W.; Vargas, W.; Ruhlandt- 2005 − *M.W.: fax, +49 (0) 3641 9-48102; e-mail, [email protected]. Senge, K. Inorg. Chem. , 44, 4862 4870. (c) Vargas, W.; Englich, U.; Ruhlandt-Senge, K. Inorg. Chem. 2002, 41, 5602−5608. Author Contributions § (d) Kennedy, A. R.; Mulvey, R. E.; Schulte, J. H. Acta Crystallogr. − These authors contributed equally. 2001, C57, 1288 1289. See also related Me2Si(NDipp)2Ae(thf)n: Notes Yang, D.; Ding, Y.; Wu, H.; Zheng, W. Inorg. Chem. 2011, 50, 7698− The authors declare no competing financial interest. 7706. (8) Gartner,̈ M.; Fischer, R.; Langer, J.; Görls, H.; Walther, D.; ■ ACKNOWLEDGMENTS Westerhausen, M. Inorg. Chem. 2007, 46, 5118−5124. (9) Glock, C.; Görls, H.; Westerhausen, M. Inorg. Chem. 2009, 48, We are very grateful to Rainer Beckert and Roman Goy for 394−399. valuable discussions as well as to the undergraduate student (10) Glock, C.; Görls, H.; Westerhausen, M. Inorg. Chim. Acta 2011, Thomas Gallert for support in the frame of an advanced 374, 429−434. laboratory course. The infrastructure of our institute was (11) Gartner,̈ M.; Görls, H.; Westerhausen, M. Inorg. Chem. 2007, 46, provided by the EU (European Regional Development Fund, 7678−7683. EFRE) and the Friedrich Schiller University Jena. Computing (12) Gartner,̈ M.; Görls, H.; Westerhausen, M. 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s‑Block-Metal-Mediated Hydroamination of Diphenylbutadiyne with Primary Arylamines Using a Dipotassium Tetrakis(amino)calciate Precatalyst Fadi M. Younis, Sven Krieck, Helmar Görls, and Matthias Westerhausen* Institute of Inorganic and Analytical Chemistry, Friedrich-Schiller-University, Humboldtstraße 8, D-07743 Jena, Germany

*S Supporting Information

ABSTRACT: The hydroamination of diphenylbutadiyne with primary arylamines requires a reactive catalyst. In the presence of heterobimetallic K2[Ca{N(H)Dipp}4] (Dipp = 2,6-diisopropylphenyl) the performance of this reaction in THF yields 2-tert-butyl-6,7,10,11-tetraphenyl-9H-cyclohepta[c]- quinoline (1a) and 2-fluoro-6,7,10,11-tetraphenyl-9H-cyclohepta[c]quinoline (1b) within 3 days at room temperature when 4-tert-butyl- and 4- fluoroaniline, respectively, have been used. During this catalysis o-CH activation occurs and quinoline derivatives are formed. Blocking the o-CH positions by methyl groups and use of 2,4,6-trimethylaniline under similar reaction conditions leads to the formation of N-mesityl-7-(E)-((mesitylimino)(phenyl)methyl)-2,3,6-triphenylcyclohepta-1,3,6- trienylamine (2) containing a β-diketimine unit with a N−H···N hydrogen bridge. NMR experiments with labeled 4-tert- butylaniline verify the transfer of N-bound hydrogen atoms to the newly formed cycloheptatriene ring. If the s-block-metal- mediated hydroamination of diphenylbutadiyne is performed in refluxing THF for 6 days, N-aryl-2,5-diphenylpyrroles 3a−d (3a, R = tBu, R′ =H;3b,R=F,R′ =H;3c,R=R′ = Me; 3d,R=R′ = H) are obtained regardless of the substitution pattern of the arylamines.

■ INTRODUCTION by deprotonation and formation of the much more aggressive − 2− Metal-mediated hydroamination of CC and CC multiple and nucleophilic amides (R2N ) or even imides (RN )of bonds with amines (Scheme 1) represents an atom-economical early transition metals or s-block metals. The disadvantageous entropy value can be minimized by an intramolecular Scheme 1. Hydroamination of Alkenes (Top) and Alkynes hydroamination reaction, leading to cyclic amines. (Bottom) Yielding Alkylamines and E/Z-Alkenylamines Alkali-metal and alkaline-earth-metal complexes represent less common catalysts for diverse reasons. Organometallics of these s-block metals contain very heteropolar metal−carbon or −

Publication Date (Web): July 7, 2015 | doi: 10.1021/acs.organomet.5b00449 metal nitrogen bonds, and saltlike ionic contributions dominate the reaction pattern. In contrast to covalent bonds, electrostatic forces are nondirectional and hence control of stereochemistry has to be performed with a definite and

Downloaded by THURINGER UNIV LANDESBIBLIOTHEK on August 28, 2015 | http://pubs.acs.org particularly designed ligand sphere. The larger alkaline-earth- metal ions are isoelectronic with trivalent ions of the scandium group as well as tetravalent ions of the titanium group, and such 0 2 procedure to prepare substituted amines by addition of N−H d metal ions are able to use d orbitals in bonding situations. bonds to alkenes or alkynes.1 Generally, this process has to Due to this fact, the heavier alkaline-earth metals combine the overcome certain challenges such as unfavorable entropic advantageous properties of typical s-block metals (strongly effects, electrostatic repulsion between a strongly Lewis basic ionic and highly heteropolar bonds, high reactivity, and amine and an electron-rich multiple bond, and lack of nucleophilicity) and early transition metals (d orbital significant exothermic reaction enthalpy. Due to these facts participation, Lewis acidity, catalytic behavior), with calcium being the ideal element because it is also globally abundant, several strategies have been developed to support the addition 3−5 of N−H functionalities to C−C multiple bonds. On the one available worldwide, inexpensive, and nontoxic. hand, activation of alkenes and alkynes often succeeds in the For about ten years, intramolecular calcium-mediated vicinity of late transition metals by back-donation of charge hydroamination of alkenes has been investigated intensely by from the metal-centered d orbitals into π* orbitals of the several research groups, often employing heteroleptic com- alkenes and alkynes, in agreement with the Dewar−Chatt− Duncanson model. On the other hand, the amines can be Received: May 7, 2015 activated by oxidative addition to transition-metal complexes or Published: July 7, 2015

© 2015 American Chemical Society 3577 DOI: 10.1021/acs.organomet.5b00449 Organometallics 2015, 34, 3577−3585 Organometallics Article

plexes with one bulky protecting anion in order to partially The copper-catalyzed addition of primary amines to − shield the catalyst.6 13 Intermolecular hydroamination reac- diphenylbutadiyne gives pyrroles in high yields. This reaction tions catalyzed by calcium-based complexes are much more requires high catalyst loads such as 25 mol % of copper(I) challenging. Therefore, amines have been added to activated halide and enhanced reaction temperatures.19 alkenes such as styrenes14,15 or carbodiimides16 as well as These results initiated a detailed investigation of the reaction alkynes14,17,18 catalyzed by amidocalcium species. These studies of primary anilines with diphenylbutadiyne in the presence of showed that the reactivity of the catalyst can be enhanced by the same approved precatalyst K2[Ca{N(H)Dipp}4] under using heterobimetallic potassium tetrakis(amido)calciates of the variation of the reaction conditions and the substitution pattern ′ type K2[Ca(NRR )4] in ethereal solvents. However, side of the primary arylamine. We decided to maintain this -products have been observed that result from an o-hydrogen precatalyst because (i) its preparation is straightforward from − activation and abstraction followed by C C bond formation the metathesis reaction of KN(H)Dipp with CaI2 (eq 1) and (Figure 1, top).18 Thus, the addition of diphenylamine to (ii) its purification easily succeeds by recrystallization. Furthermore, (iii) this compound crystallizes free of solvent, thus avoiding aging of the solid by uncontrolled loss of solvent molecules; hence, stoichiometric requirements (addition of a fi speci ed mole percent of K2[Ca{N(H)Dipp}4]tothe substrates) can easily be achieved.

+Cal2 4KN(H)Dipp⎯→⎯⎯⎯⎯ K2 [Ca{N(H)Dipp]4 −2Kl (1)

■ RESULTS AND DISCUSSION Synthesis. In a typical procedure, equimolar amounts of diphenylbutadiyne and substituted amine were combined in tetrahydrofuran (THF) in the presence of 5 mol % of K2[Ca{N(H)Dipp}4] and stirred for 3 days at room temper- ature. Depending on the substitution pattern, different reaction pathways have been observed. The use of 4-tert-butylaniline in this reaction and a hydrolytic workup procedure yields product 1a regardless of the applied stoichiometry. This product is based on α-deprotonation steps of 4-tert-butylaniline and formation of a C−C bond leading to 2-tert-butyl-6,7,10,11- tetraphenyl-9H-cyclohepta[c]quinoline (1a); very poor yields were obtained under similar reaction conditions for the reaction of diphenylbutadiyne with 4-fluoroaniline leading to 2-fluoro- 6,7,10,11-tetraphenyl-9H-cyclohepta[c]quinoline (1b). The fluoro substituent withdraws electron density via the aromatic ring from the nitrogen atom, reducing the nucleophilicity of the amino functionality. Compensation of reduced reactivity by more drastic reaction conditions proved to be disadvantageous because at raised temperatures another reaction pathway was observed as discussed below, yielding a pyrrole. Nevertheless, Publication Date (Web): July 7, 2015 | doi: 10.1021/acs.organomet.5b00449 Figure 1. Products of the s-block-metal-mediated hydroamination of derivatives 1a,b both represent quinoline derivatives with diphenylbutadiyne with N-diisopropylaniline (top) and 2,6-diisopro- annelated seven-membered rings. The reaction is depicted in eq pylaniline (bottom; only the formerly N-bound H atoms are depicted), 2, and only hydrogen atoms that are involved in the conversion containing 2 equiv of butadiyne (yellow and green) and 1 equiv of are explicitly shown. Downloaded by THURINGER UNIV LANDESBIBLIOTHEK on August 28, 2015 | http://pubs.acs.org amine (C, gray; N, blue).

diphenylbutadiyne required a heterobimetallic s-block-metal catalyst, whereas the addition of more nucleophilic N- isopropylaniline to this butadiyne can be promoted by homometallic s-block-metal amides. In contrast to this “simple” addition of a N−H bond of a secondary amine to diphenylbutadiyne, the reaction of primary 2,6-diisopropylani- line with diphenylbutadiyne at room temperature in the presence of catalytic amounts of K2[Ca{N(H)Dipp}4] (Dipp = 2,6-diisopropylphenyl) proceeds via multiple reaction steps The reaction of 2,4,6-trimethylaniline with diphenylbuta- involving ring expansion of the 2,6-diisopropylphenyl ring to a diyne must proceed via a different pathway, because the ortho seven-membered-ring system (Figure 1, bottom).17 Here, 2 positions are blocked by methyl groups. In this case, a 1:1 ratio equiv of diphenylbutadiyne (distinguished by the colors yellow of both substrates was observed at room temperature in THF and green) react with 1 equiv of H2N-Dipp, regardless of the with a precatalyst load of 5 mol % of K2[Ca{N(H)-Dipp}4] applied stoichiometry. according to eq 3, yielding N-mesityl-7-(E)-((mesitylimino)-

3578 DOI: 10.1021/acs.organomet.5b00449 Organometallics 2015, 34, 3577−3585 Organometallics Article

Scheme 2. Proposed Mechanism of the s-Block-Metal- Mediated Hydroamination of Diphenylbutadiyne with Primary Arylamines at High Temperatures Yielding N-Aryl- 2,5-diphenylpyrroles

(phenyl)methyl)-2,3,6-triphenylcyclohepta-1,3,6-trienylamine (2). Only those hydrogen atoms are depicted that were bound at the nitrogen atom of the amine substrate. Again, a seven- membered cycloheptatriene moiety was found; however, the mesityl substituents remain intact during this transformation, in contrast to earlier findings with 2,6-diisopropylaniline yielding product B (Figure 1, bottom).17 In order to study the influence of the reaction temperature, in a typical procedure diphenylbutadiyne was dissolved in THF and an equimolar amount of arylamine and 5 mol % of the catalyst K2[Ca{N(H)Dipp}4] were added. This reaction fl mixture was stirred and re uxed for 3 days. Then another 5 heterobimetallic catalyst system.17,18 E/Z isomerization is mol % of K2[Ca{N(H)Dipp}4] was added and heating was possible via the cumulene isomer A′, which can isomerize to continued for a further 3 days. A standard workup procedure either a trans (A) or a cis orientation (A″) of the anionic site including hydrolysis with distilled water, extraction with diethyl and the remaining alkyne moiety. Such cumulene systems have ether, drying with sodium sulfate, and recrystallization from also been suggested during calcium-mediated hydrophospha- ° pentane or toluene at 5 C yielded colorless crystals of N-aryl- nylation of diphenylbutadiyne with diphenylphosphane in order ′ 2,5-diphenylpyrroles 3 according to eq 4 (3a,R=tBu, R =H; to explain isomer mixtures.20 After the initial reaction step, ′ ′ ′ 3b,R=F,R =H;3c,R=R = Me; 3d,R=R = H). intramolecular metalation transfers the N-bound hydrogen to the alkenyl moiety and amide B is formed. During the high- temperature route an intramolecular addition to the second alkyne unit occurs and the pyrrole derivative C is formed. The reaction of this intermediate species with another arylamine regenerates the catalyst, and the formation of pyrroles 3a−d is completed. In contrast to this straightforward pathway for the synthesis of pyrroles 3a−d, the low-temperature route proceeds via an insertion of another diphenylbutadiyne molecule into the metal−carbon bond of the primary reaction product (carbometalation step, Scheme 3) yielding intermediate D. For the sake of clarity the diphenylbutadiyne units are Proposed Mechanism. ff

Publication Date (Web): July 7, 2015 | doi: 10.1021/acs.organomet.5b00449 In all cases, with the exception of distinguished by di erent colors in this scheme. An intra- 1b, moderate to good yields were obtained. The precatalyst molecular metalation reaction forms amide E. Now, two K2[Ca{N(H)Dipp}4] reacts with the primary aniline substrate, reaction routes seem to be feasible to explain the formation of 1 and NMR spectroscopic investigations of THF solutions (via o-CH activation) and 2 (via addition of a second containing K [Ca{N(H)-Dipp} ] and the 4-fold stoichiometric arylamine). These compounds are depicted in Figure 2, also Downloaded by THURINGER UNIV LANDESBIBLIOTHEK on August 28, 2015 | http://pubs.acs.org 2 4 amount of 2,4,6-trimethylaniline verified the quantitative ligand clarifying the origin of the structural moieties. The closed-shell exchange and formation of 2,6-diisopropylaniline. A 1:2 ratio of ionic mechanism involves the formation of the 1,2,4,6- K2[Ca{N(H)Dipp}4] and mesitylamine led to heteroleptic cycloheptatetraene intermediate F. Such species exhibit ring calciates of the general formula K2[Ca{N(H)Dipp}4−x{N(H)- strain; nevertheless, unsaturated ring systems of this kind have 21 Mes}x]. Due to the fact that all aniline derivatives might exhibit already been studied in a solid matrix and by quantum comparable pKa values, it can be concluded that the bulkier chemical investigations, also considering other isomers such as amide is replaced by the smaller amide in order to minimize phenylcarbene, bicyclo[3.2.0]hepta-1,3,6-triene, bicyclo[3.2.0]- intramolecular strain of the calciate anion mainly provoked by hepta-3,6-diene-2-ylidene, bicyclo[3.2.0]hepta-2,3,6-triene, and the ortho substituents. bicyclo[4.1.0]heptatriene.22 Furthermore, a cyclotetramer of The catalytic reaction starts with the addition of a metal− such a strained cycloheptatetraene derivative has been nitrogen bond to one CC triple bond as shown in Scheme 2 characterized by an X-ray crystal structure determination.23 (nucleophilic attack of an amide at an alkyne) yielding Despite the fact that ring strain is present in cycloheptate- intermediate A. In this scheme, M symbolizes the s-block traenes, these derivatives also represent 4n π-Möbius aromatic metal and hence the anionic site. The reactivity of systems.24 Intermolecular metalation by an arylamine regener- homometallic calcium amides is not sufficient to mediate this ates the catalyst and leads to the formation of G. hydroamination. Therefore, we employed the already known In this bicyclic intermediate G the allene moiety attacks the strategy to significantly enhance the reactivity by formation of a o-CH group leading to compound 1. Absence of o-CH

3579 DOI: 10.1021/acs.organomet.5b00449 Organometallics 2015, 34, 3577−3585 Organometallics Article

Scheme 3. Proposed Mechanism of the s-Block-Metal- Mediated Hydroamination of Diphenylbutadiyne with Primary Arylamines at Room Temperature via a 1,2,4,6- Cycloheptatetraene Intermediate and via a Bergman a Cyclization Route

Figure 2. Stick-and-ball presentations of 1 (top) and 2 (bottom). The structural building blocks are distinguished by different colors: the initial diphenylbutadiyne moieties are shown in yellow and green and the arylamines in gray (C atoms) and blue (N atom). Only those H atoms are drawn (light gray) that are involved in chemical transformations or are bound at a nitrogen atom.

Scheme 4. Proposed Final Mechanistic Steps for the a Formation of 2 Starting from I or G′ Publication Date (Web): July 7, 2015 | doi: 10.1021/acs.organomet.5b00449 Downloaded by THURINGER UNIV LANDESBIBLIOTHEK on August 28, 2015 | http://pubs.acs.org

aThe diphenylbutadiyne units are distinguished by the colors orange and green.

fragments and bulkier N-bound aryl groups favor the formation aG′ is the E isomer of G. of isomer G′ (Scheme 4), leading to an alternative reaction pattern. Here, the 1,4-addition of an arylamine to the cycloheptatetraene ring leads to the formation of compound 2. The fact that homometallic calcium bis(amide) does not An alternative pathway contains the Bergman cyclization mediate these hydroamination reactions raises the question of leading to diradical H. Again the catalyst is re-formed by an the cooperation of potassium and calcium in the catalyst intermolecular reaction with an arylamine yielding intermediate system. In the solid state K2[Ca{N(H)Dipp}4] forms a 2− I. This radical can attack either at a o-CH group (yielding 1) coordination polymer consisting of [Ca{N(H)Dipp}4] orin the case that such a functionality is absentanother anions interconnected by potassium cations.17 It can be amine substrate, leading to compound 2 as shown in Scheme 4. assumed that in solution the calciate anions are maintained.

3580 DOI: 10.1021/acs.organomet.5b00449 Organometallics 2015, 34, 3577−3585 Organometallics Article

In these calciate anions electrostatic repulsion between the amido substituents enhances the Ca−N bond lengths and, hence, the nucleophilicity and reactivity of the amido groups. This consideration suggests that M in the schemes might be a calciate fragment. The role of the potassium ions remains unclear and speculative. Potassium ions are considered as soft Lewis acids, being able to coordinate to rather hard (such as ethers) and preferably to soft Lewis bases such as aromatics and extended π systems. Nevertheless, it remains speculative to what extent this coordination behavior of K+ supports the catalytic hydroamination via coordination to any of the reported intermediates. Due to the fact that rather high yields of the products were obtained and that cycloheptatetraene derivatives have already been accessible experimentally, we favor the mechanism via the cycloheptatetraene intermediates. In addition, we would expect diverse derivatives for the radical mechanism due to reactions of the radical with solvent molecules and still present arylamine substrates. NMR Experiments. The 1H NMR spectrum of 1a (R = tBu) clearly shows a characteristic ABX coupling pattern for the hydrogen atoms at the seven-membered ring leading to three doublets of doublets (Figure 3) with a pseudotriplet for the CH

Figure 4. 1H NMR spectrum of the CH fragment of the seven- membered ring of partially deuterated 1a (top), with assignment to differently deuterated derivatives (bottom).

tert-butylphenyl group to the seven-membered ring yielding the methylene group. Compound 2 represents a β-diketimine derivative with an annelated unsaturated seven-membered ring. This structural fragment gives rise to a low-field-shifted resonance for the N− ··· δ 1 H N hydrogen bridge with a chemical shift of 12.85 ppm. In Figure 3. H NMR resonances of the newly formed methylene unit of Figure 5 the 1H NMR spectrum of the methyl region is the seven-membered ring of compound 1a. The coupling pattern clearly verifies the magnetic nonequivalence of the H atoms. Publication Date (Web): July 7, 2015 | doi: 10.1021/acs.organomet.5b00449 resonance at δ 6.41 ppm due to very similar vicinal coupling constants. The H atoms of the methylene fragment are magnetically inequivalent with a geminal coupling constant of 2J = 11.6 Hz, verifying the nonplanarity of the cyclo-

Downloaded by THURINGER UNIV LANDESBIBLIOTHEK on August 28, 2015 | http://pubs.acs.org HH heptatriene unit. In order to support the reaction mechanism, we repeated the preparation of this compound with partially N-deuterated 4- tert-butylaniline with a deuteration degree of 75%. This approach should yield 1a in addition to its partially deuterated 1 derivatives. The coupling pattern in the H NMR spectrum at 1 the CH signal at δ = 6.41 ppm enables the assignment and Figure 5. H NMR resonances of the methyl substituents of the determination of the positions of deuterium atoms (Figure 4). mesityl groups, showing that the 2,6-positions are magnetically  − − nonequivalent, which suggests a hindered rotation of the mesityl The coupling pattern of the endocyclic CH CH2 fragment − − − groups around the N C bonds. allows the assignment to the moieties CH CH2,CH CHD, and CH−CDH. The intensity ratio of the resonances excludes − the formation of CH CD2 units, which would suggest a bimolecular reaction mechanism. This coupling pattern and the depicted. All methyl groups are chemically different, which has resonances of the neighboring methylene group (see the been explained by hindered rotation around the C−N bonds. Supporting Information) clearly show that there exists no The nonequivalence of the o-methyl groups of each mesityl preference for deuteration at either position and hence no substituent is a consequence of the chiral carbon atom of the stereocontrol for the transfer of the o-hydrogen atom of the 4- seven-membered cycloheptatriene ring.

3581 DOI: 10.1021/acs.organomet.5b00449 Organometallics 2015, 34, 3577−3585 Organometallics Article

Molecular Structures. The molecular structure and numbering scheme of N-mesityl-2,5-diphenylpyrrole (3c) are depicted in Figure 6. Due to steric reasons the N-bound aryl

Figure 7. Molecular structure and numbering scheme of 1a. The ellipsoids represent a probability of 30%, Hand atoms are shown with Figure 6. Molecular structure and numbering scheme of 3c. The arbitrary radii. Selected bond lengths are given in Table 1. ellipsoids represent a probability of 30%, and H atoms are shown with arbitrary radii. Selected bond lengths (pm): N1−C1 139.1(2), N1−C4 139.3(2), N1−C11 144.4(2), C1−C2 138.1(2), C2−C3 140.7(2), C3−C4 137.8(2), C1−C20 147.6(2), C4−C5 146.8(2). Selected bond angles (deg): C1−N1−C4 109.0(1), N1−C1−C2 107.5(1), C1−C2− C3 107.9(1), C2−C3−C4 108.4(1), N1−C4−C3 107.3(1), C1−N1− C11 125.6(1), C4−N1−C11 125.1(1), N1−C1−C20 124.7(1), C2− C1−C20 127.8(1), N1−C4−C5 125.3(1), C3−C4−C5 127.4(1).

group is oriented nearly perpendicular to the pyrrole ring with an angle of 69.2° between these planes. Expectedly, the π system of the pyrrole ring leads to short bonds and charge delocalization to a large extent. Endocyclic C1−C2, C2−C3, and C3−C4 bond lengths differ by less than 3 pm and have an average value of 138.9 pm. The exocyclic C1−C20 and C4−C5 bond lengths, with an average distance of 147.2 pm, are characteristic for single bonds between sp2-hybridized carbon atoms. 1,2,5-Triphenylpyrrole (3d) exhibits crystallographic C2 symmetry and shows very similar structural parameters (see the Supporting Information). This measurement at −140 °C leads Figure 8. Molecular structure and numbering scheme of 1b. The to results very similar to those of the crystal structure ellipsoids represent a probability of 30%, and H atoms are shown with determination at room temperature.25 arbitrary radii. Selected bond lengths are given in Table 1. Verification of the compositions of 1a,b and 2 as shown in Publication Date (Web): July 7, 2015 | doi: 10.1021/acs.organomet.5b00449 Figure 2 was also successful by X-ray diffraction experiments on as well as N1B and C17B−C25B). Compound 2 contains the single crystals. Molecular structures and numbering schemes of chiral C4B atom, but due to the centric monoclinic space group 1a,b are presented in Figures 7 and 8, respectively. The the crystalline state consists of a racemate. The structure- numbering schemes of both compounds are identical, and a dominating moiety is the N1A−C1B−C2B−C3B−N1B frag- Downloaded by THURINGER UNIV LANDESBIBLIOTHEK on August 28, 2015 | http://pubs.acs.org comparison of selected bond lengths is given in Table 1. These ment with significant charge delocalization and a N1B−H··· compounds are built from two butadiyne molecules (atoms N1A hydrogen bridge (N1A···N1B distance 265.7(3) pm). The C1A−C16A and C1B−C16B) and one 4-tert-butylaniline C1A−C2B bond length shows a characteristic single-bond (N1A, C17A−C26A) or 4-fluoroaniline molecule (N1A, F1A, value for sp2-hybridized carbon atoms excluding π interaction C17A−C22A), respectively. The quinoline fragments show between the β-diketimine unit and the remaining π bonds of balanced bond lengths which are comparable to those of the seven-membered ring. This hydrogen bridge also explains unsubstituted quinoline.26 Substituents at the quinoline nucleus why only the E isomer of the N1AC1B imine unit is of 1a,b lead to a slight lengthening between those carbon atoms observed. carrying substituents. The phenyl groups are oriented nearly perpendicular to the ring systems; hence, no interaction ■ CONCLUSION between the aromatic phenyl groups and the π-systems of the The s-block-metal-mediated hydroamination of diphenylbuta- seven-membered ring can be expected and characteristic C−C diyne with primary amines in THF requires the presence of 5− single bond values around 149 pm were observed. 10 mol % of heterobimetallic K2[Ca{N(H)Dipp}4]; homo- The molecular structure and numbering scheme of metallic calcium bis(amides) did not initiate the hydro- compound 2 are shown in Figure 9. This compound is built amination under similar reaction conditions. The substitution from two butadiyne (atoms C1A−C4A and C1B to C4B) and pattern of the arylamines and the reaction conditions strongly two 2,4,6-trimethylaniline molecules (N1A and C17A−C25A influence the reaction pathway. At high temperatures in

3582 DOI: 10.1021/acs.organomet.5b00449 Organometallics 2015, 34, 3577−3585 Organometallics Article

Table 1. Comparison of Selected Bond Lengths (pm) of 2- These highly reactive intermediates attack o-CH functionalities tert-Butyl-6,7,10,11-tetraphenyl-9H-cyclohepta[c]quinoline of the arylamine unit, leading to a quinoline derivative with a (1a) and 2-Fluoro-6,7,10,11-tetraphenyl-9H- 2:1 ratio of butadiyne to arylamine. If o-CH groups are not cyclohepta[c]quinoline (1b) available, another reaction pathway is pursued and the reactive intermediate traps another 1 equiv of arylamine, yielding a β- bond 1a (R = tBu) 1b (R = F) diketimine derivative which is annelated to a seven-membered N1A−C1A 131.4(2) 131.4(3) ring. This β-diketimine crystallizes in the ene−amine form with N1A−C17A 137.1(2) 138.0(3) aN−H···N hydrogen bridge and shows no significant C17A−C18A 140.8(2) 141.5(3) conjugation with the attached multiple bonds of the annelated C17A−C22A 141.6(2) 141.5(3) seven-membered ring. The performance of this s-block-metal- C18A−C19A 137.0(2) 137.5(4) mediated hydroamination of diphenylbutadiyne at room C19A−C20A 141.4(2) 138.7(4) temperature allows the synthesis of quinolone derivatives in C20A−C21A 138.5(2) 136.4(3) the presence of o-CH functionalities. C20A−R 153.2(2) 136.3(3) Special attention has to be given to the advantageous C21A−C22A 141.6(2) 141.9(3) properties of the catalyst system. The reaction of 4 equiv of C1A−C2A 144.4(2) 144.2(3) KN(H)Dipp with calcium iodide in THF yields solvent-free C1A−C11A 149.1(2) 149.6(3) K [Ca{N(H)Dipp} ].17 The potassium ions bind to the amido − 2 4 C2A C3A 139.5(2) 139.5(3) anions and to the π systems of the aryl groups, leading to a − C2A C4B 148.6(2) 148.3(3) coordination polymer in the solid state. Nevertheless, this − C3A C4A 149.2(2) 148.6(3) complex is soluble in ethers. On the one hand, the rather bulky − C3A C22A 144.6(2) 146.2(3) isopropyl groups in ortho positions prevent formation of ether − C4A C5A 149.4(2) 149.4(3) adducts which commonly tend to slowly lose these neutral − C4A C1B 135.6(2) 135.8(3) coligands upon standing and handling. Partial loss of coligands − C1B C2B 151.8(2) 151.1(3) leads to weathering of the crystalline material and makes it − C1B C11B 149.0(2) 149.3(3) difficult to exactly meet the stoichiometry. On the other hand, − C2B C3B 150.3(2) 150.5(3) these isopropyl groups enhance intramolecular steric strain − C3B C4B 133.8(2) 132.8(3) which can be released by a ligand exchange reaction and, − C4B C5B 149.0(2) 149.2(3) therefore, in solution a fast substitution of the 2,6- diisopropylanilide anion by smaller amide ligands occurs. This initial amide exchange, which is much faster than the addition to the alkyne moieties, is the reason that K2[Ca{N(H)Dipp}4] represents an ideal precatalyst for any hydroamination of diphenylbutadiyne with sterically less demanding primary arylamines. It is a common observation that heterobimetallic s-block-metal compounds often adopt reactivities different from − those of their homometallic constituents.5,27 30 These mixed- metal complexes form metalates27,28 which are in some cases addressed as inverse crowns29 and turbo Grignard or turbo Hauser reagents.30 In conclusion, thermodynamic control (in boiling THF) of s- block-metal-mediated hydroamination of diphenylbutadiyne with primary arylamines employing K2[Ca{N(H)Dipp}4] yields Publication Date (Web): July 7, 2015 | doi: 10.1021/acs.organomet.5b00449 N-aryl-2,5-diphenylpyrroles regardless of the bulkiness of the Figure 9. Molecular structure and numbering scheme of 2. The N-bound aryl groups, whereas kinetic control (at room ellipsoids represent a probability of 30%, and selected H atoms are temperature) leads to rather complex reaction pathways shown with arbitrary radii. Selected bond lengths (pm): N1A−C17A − − − depending on the ortho substituents of the arylamines, where Downloaded by THURINGER UNIV LANDESBIBLIOTHEK on August 28, 2015 | http://pubs.acs.org 142.9(3), N1A C1B 129.5(3), N1B C17B 143.2(3), N1B C3B 135.7(3), N1B−H 88(3), C1A−C2A 135.8(3), C1A−C2B 147.2(3), the formation of unsaturated seven-membered rings represents C1A−C11A 149.0(3), C2A−C3A 143.9(3), C3A−C4A 134.7(3), a key feature. C4A−C5A 148.4(3), C4A−C4B 152.8(3), C1B−C2B 146.9(3), C1B−C11B 150.6(3), C2B−C3B 139.1(3), C3B−C4B 151.6(3), ■ EXPERIMENTAL SECTION C4B−C5B 153.9(3). General Remarks. All manipulations were carried out under an inert nitrogen atmosphere using standard Schlenk techniques. The refluxing THF the formation of N-aryl-2,5-diphenylpyrroles solvent was dried over KOH and subsequently distilled over sodium/ succeeds with moderate to high yields. A 2-fold addition of benzophenone under a nitrogen atmosphere prior to use. Deuterated metal−nitrogen bonds to both CC triple bonds yields solvents were dried over sodium, degassed, and saturated with pyrrole rings with an aromatic character. nitrogen. The yields given are not optimized. 1H and 13C{1H} NMR In contrast to the high-temperature route, the s-block-metal- spectra were recorded on Bruker AC 400 and AC 600 spectrometers. mediated reaction of diphenylbutadiyne with arylamines at Chemical shifts are reported in parts per million relative to SiMe4 as an external standard. The residual signals of the deuterated solvents room temperature strongly depends on the substituents in [D ]THF and CD Cl were used as internal standards. The solvent- ortho positions. During this reaction an amide reacts with two 8 2 2 free and recrystallized precatalyst K2[Ca{N(H)Dipp}4] was prepared diphenylbutadiyne molecules. Cyclization leads either to a according to a literature procedure.17 A specific amount of this cyclohepta-1,2,4,6-tetraene intermediate or, via Bergman compound was dissolved in anhydrous THF, and aliquots of this cyclization, to a methylidene−cycloheptatrienediyl radical. solution were added to the reaction mixtures. This procedure allowed

3583 DOI: 10.1021/acs.organomet.5b00449 Organometallics 2015, 34, 3577−3585 Organometallics Article

us to easily add definite amounts of precatalyst to the substrates under Notes strictly anaerobic conditions. All substrates were purchased from The authors declare no competing financial interest. Sigma-Aldrich, Merck, or Alfa Aesar and used without further purification. General Procedure for the Synthesis of 2-Substituted ■ ACKNOWLEDGMENTS 6,7,10,11-Tetraphenyl-9H-cyclohepta[c]quinolone (1; R = tBu, F). This paper is dedicated to Professor Manfred Scheer on the A 2 equiv amount of diphenylbutadiyne was dissolved in THF. fi Thereafter, 1 equiv of 4-tert-butylaniline and 5 mol % (with respect to occasion of his 60th birthday. We appreciate the nancial the butadiyne) of the catalyst K2[Ca{N(H)Dipp}4]∞ were added. This support of the Fonds der Chemischen Industrie im Verband solution was stirred for 3 days at room temperature. After hydrolysis der Chemischen Industrie e.V. (FCI/VCI, Frankfurt/Main, with distilled water, extraction with diethyl ether, drying with sodium Germany). F.M.Y. thanks the German Academic Exchange sulfate, and recrystallization from a mixture of dichloromethane and Service (DAAD, Bonn, Germany) for a generous Ph.D. stipend. pentane at 5 °C, colorless crystals were isolated from an orange mother liquor. Synthesis of 2. Diphenylbutadiyne (0.3 g 1.48 mmol) was ■ REFERENCES dissolved in 15 mL of THF. Then, 0.21 mL of 2,4,6-trimethylaniline (1) (a) Hydrofunctionalization; Ananikov, V. P., Tanaka, M., Eds.; (0.2 g, 1.48 mmol) and 5 mol % of the calciate catalyst Springer: Heidelberg, Germany, 2013; Topics in Organometallic K2[Ca{N(H)Dipp}4]∞ were added. This reaction mixture was stirred Chemistry 43. (b) Behr, A.; Neubert, P.: Applied Homogeneous for 3 days at oom temperature. A standard workup procedure included Catalysis; Wiley-VCH: Weinheim, Germany, 2012; Chapter 30, pp hydrolysis with 15 mL of distilled water, extraction with diethyl ether, 455−472. (c) Catalyzed Carbon-Heteroatom Bond Formation; Yudin, drying with sodium sulfate, and recrystallization from a mixture of ̈ ° A. K., Ed.; Wiley-VCH: Weinheim, Germany, 2011. (d) Muller, T. E.; dichloromethane and pentane at 5 C, yielding colorless crystals in a Hultzsch, K. C.; Yus, M.; Foubelo, F.; Tada, M. Chem. Rev. 2008, 108, reddish brown mother liquor. Yield: 0.4 g, 0.59 mmol, 80%. − N 3795 3892. (e) Catalytic Heterofunctionalization: From Hydroamina- General Procedure for the Synthesis of -Aryl-2,5-diphe- ̈ nylpyrroles 3. Diphenylbutadiyne (0.3 g 1.48 mmol) was dissolved in tion to Hydrozirconization; Togni, A., Grutzmacher, H., Eds.; Wiley- 17 mL of THF before 4-fluoraniline (0.164 g, 1.48 mmol) and 10 mol VCH: Weinheim, Germany, 2001. (2) (a) Kaupp, M. In Anorganische Chemie: Prinzipien von Struktur % of the calciate K2[Ca{N(H)Dipp}4]∞ (5 mol % at the beginning ̈ and 5 mol % after 3 days) were added, and the reaction mixture was und Reaktivitat; Huheey, J. E., Keiter, E. A., Keiter, R. L., Eds.; De ° Gruyter: Berlin, Boston, 2012. (b) Kaupp, M. Angew. Chem., Int. Ed. heated for 6 days at 60 C. Thereafter, the solution was hydrolyzed − with 15 mL of distilled water and extracted with diethyl ether and the 2001, 40, 3534 3565. − separated ether phase dried with sodium sulfate. Recrystallization from (3) Harder, S. Chem. Rev. 2010, 110, 3852 3876. pentane at 5 °C yielded a colorless solid (0.40 g, 1.27 mmol, 85.8%) in (4) (a) Crimmin, M. R.; Hill, M. S. Top. Organomet. Chem. 2013, 45, − an orange mother liquor. 191 241. (b) Barrett, A. G. M.; Crimmin, M. R.; Hill, M. S.; − X-ray Structure Determination. The intensity data for the Procopiou, P. A. Proc. R. Soc. London, Ser. A 2010, 466, 927 963. compounds were collected on a Nonius KappaCCD diffractometer (5) Westerhausen, M.; Langer, J.; Krieck, S.; Glock, C. Rev. Inorg. using graphite-monochromated Mo Kα radiation. Data were corrected Chem. 2011, 31, 143−184. for Lorentz and polarization effects; absorption was taken into account (6) (a) Romero, N.; Rosca,̧ S.-C.; Sarazin, Y.; Carpentier, J.-F.; − on a semiempirical basis using multiple scans.31 33 The structures Vendier, L.; Mallet-Ladeira, S.; Dinoi, C.; Etienne, M. Chem. - Eur. J. were solved by direct methods (SHELXS)34 and refined by full-matrix 2015, 21, 4115−4125. (b) Liu, B.; Roisnel, T.; Carpentier, J.-F.; 2 34 − least-squares techniques against Fo (SHELXL-97). The hydrogen Sarazin, Y. Chem. - Eur. J. 2013, 19, 13445 13462. (c) Liu, B.; Roisnel, atoms (with the exception of methyl groups C24, C25, and C26 of 1a T.; Carpentier, J.-F.; Sarazin, Y. Chem. - Eur. J. 2013, 19, 2784−2802. and 2) were located by difference Fourier synthesis and refined (7) (a) Mathia, F.; Zalupsky, P.; Szolcsanyi, P. Targets Heterocycl. isotropically. All non-hydrogen atoms were refined anisotropically.34 Systems 2012, 16, 309−370. (b) Mathia, F.; Zalupsky, P.; Szolcsanyi, P. Crystallographic data as well as structure solution and refinement Targets Heterocycl. Systems 2011, 15, 226−262. details are summarized in the Supporting Information. The programs (8) (a) Nixon, T. D.; Ward, B. D. Chem. Commun. 2012, 48, 11790− XP (Siemens Analytical X-ray Instruments, Inc.)35 and POV-Ray36 11792. (b) Wixey, J. S.; Ward, B. D. Dalton Trans. 2011, 40, 7693− were used for structure representations. 7696. (c) Wixey, J. S.; Ward, B. D. Chem. Commun. 2011, 47, 5449− Publication Date (Web): July 7, 2015 | doi: 10.1021/acs.organomet.5b00449 5451. ■ ASSOCIATED CONTENT (9) (a) Jenter, J.; Koeppe, R.; Roesky, P. W. Organometallics 2011, − * 30, 1404 1413. (b) Panda, T. K.; Hrib, C. G.; Jones, P. G.; Jenter, J.; S Supporting Information Roesky, P. W.; Tamm, M. Eur. J. Inorg. Chem. 2008, 2008, 4270−4279.

Downloaded by THURINGER UNIV LANDESBIBLIOTHEK on August 28, 2015 | http://pubs.acs.org Text, figures, a table, and CIF files giving preparative details and (c) Datta, S.; Garner, M. T.; Roesky, P. W. Organometallics 2008, 27, physical data of all reported compounds and crystallographic 1207−1213. (d) Datta, S.; Roesky, P. W.; Blechert, S. Organometallics data of the crystal structure determinations as well as the NMR 2007, 26, 4392−4394. spectra of all new compounds. The Supporting Information is (10) (a) Arrowsmith, M.; Crimmin, M. R.; Barrett, A. G. M.; Hill, M. S.; Kociok-Kohn, G.; Procopiou, P. A. Organometallics 2011, 30, available free of charge on the ACS Publications website at − DOI: 10.1021/acs.organomet.5b00449. Crystallographic data 1493 1506. (b) Crimmin, M. R.; Arrowsmith, M.; Barrett, A. G. M.; (excluding structure factors) have also been deposited with the Casely, I. J.; Hill, M. S.; Procopiou, P. A. J. Am. Chem. Soc. 2009, 131, 9670−9685. (c) Arrowsmith, M.; Hill, M. S.; Kociok-Kohn, G. Cambridge Crystallographic Data Centre as supplementary Organometallics 2009, 28, 1730−1738. (d) Barrett, A. G. M.; Crimmin, publications CCDC-1062187 for 1a, CCDC-1062188 for 1b, M. R.; Hill, M. S.; Hitchcock, P. B.; Kociok-Kohn, G.; Procopiou, P. A. CCDC-1062189 for 2, CCDC-1062190 for 3c, and CCDC- Inorg. Chem. 2008, 47, 7366−7376. (e) Crimmin, M. R.; Casely, I. J.; 1062191 for 3d. Copies of the data can be obtained free of Hill, M. S. J. Am. Chem. Soc. 2005, 127, 2042−2043. charge on application to the CCDC, 12 Union Road, (11) (a) Mukherjee, A.; Nembenna, S.; Sen, T. K.; Sarish, S. P.; Cambridge CB2 1EZ, U.K. (e-mail [email protected]). Ghorai, P. K.; Ott, H.; Stalke, D.; Mandal, S. K.; Roesky, H. W. Angew. Chem., Int. Ed. 2011, 50, 3968−3972. (b) Roesky, P. W. Angew. Chem., ■ AUTHOR INFORMATION Int. Ed. 2009, 48, 4892−4894. (12) Neal, S. R.; Ellern, A.; Sadow, A. D. J. Organomet. Chem. 2011, Corresponding Author 696, 228−234. *M.W.: fax, +49 (0) 3641 9-48132; e-mail, [email protected]. (13) Buch, F.; Harder, S. Z. Naturforsch. 2008, 63b, 169−177.

3584 DOI: 10.1021/acs.organomet.5b00449 Organometallics 2015, 34, 3577−3585 Organometallics Article

(14) (a) Reid, S.; Barrett, A. G. M.; Hill, M. S.; Procopiou, P. A. Org. (33) SADABS 2.10, Bruker-AXS Inc., Madison, WI, USA, 2002. Lett. 2014, 16, 6016−6019. (b) Brinkmann, C.; Barrett, A. G. M.; Hill, (34) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. M. S.; Procopiou, P. A. J. Am. Chem. Soc. 2012, 134, 2193−2207. 2008, 64, 112−122. (15) Barrett, A. G. M.; Brinkmann, C.; Crimmin, M. R.; Hill, M. S.; (35) XP; Siemens Analytical X-ray Instruments Inc., Karlsruhe, Hunt, P.; Procopiou, P. A. J. Am. Chem. Soc. 2009, 131, 12906−12907. Germany, 1990, and Madison, WI, USA, 1994. (16) (a) Al-Shboul, T. M. A.; Volland, G.; Görls, H.; Westerhausen, (36) POV-Ray, Persistence of Vision Raytracer: Victoria, Australia, M. Z. Anorg. Allg. Chem. 2009, 635, 1568−1572. (b) Lachs, J. R.; 2007. Barrett, A. G. M.; Crimmin, M. R.; Kociok-Kohn, G.; Hill, M. S.; Mahon, M. F.; Procopiou, P. A. Eur. J. Inorg. Chem. 2008, 2008, 4173− 4179. (17) Glock, C.; Younis, F. M.; Ziemann, S.; Görls, H.; Imhof, W.; Krieck, S.; Westerhausen, M. Organometallics 2013, 32, 2649−2660. (18) Glock, C.; Görls, H.; Westerhausen, M. Chem. Commun. 2012, 48, 7094−7096. (19) Dudnik, A. S.; Gevorgyan, V. In Catalyzed Carbon-Heteroatom Bond Formation; Yudin, A. K., Ed.; Wiley-VCH: Weinheim, Germany, 2011; Chapter 8, pp 227−316. (20) Al-Shboul, T. M. A.; Palfi,́ V. K.; Yu, L.; Kretschmer, R.; Wimmer, K.; Fischer, R.; Görls, H.; Reiher, M.; Westerhausen, M. J. Organomet. Chem. 2011, 696, 216−227. (21) (a) McKee, M. L.; Reisenauer, H. P.; Schreiner, P. R. J. Phys. Chem. A 2014, 118, 2801−2809. (b) Warmuth, R.; Marvel, M. A. Chem. - Eur. J. 2001, 7, 1209−1220. (c) Matzinger, S.; Bally, T. J. Phys. Chem. A 2000, 104, 3544−3552. (22) (a) Yang, Z. Y.; Wang, X. L.; Wang, J.; Zhang, J. C.; Cao, W. L. Chin. Chem. Lett. 2005, 16, 1417−1420. (b) Patterson, E. V.; McMahon, R. J. J. Org. Chem. 1997, 62, 4398−4405. (23) Mahlokozera, T.; Goods, J. B.; Childs, A. M.; Thamattoor, D. M. Org. Lett. 2009, 11, 5095−5097. (24) Martin-Santamaria, S.; Lavan, B.; Rzepa, H. S. Chem. Commun. 2000, 1089−1090. (25) Feng, X.; Tong, B.; Shen, J.; Shi, J.; Han, T.; Chen, L.; Zhi, J.; Lu, P.; Ma, Y.; Dong, Y. J. Phys. Chem. B 2010, 114, 16731−16736. (26) Davies, J. E.; Bond, A. D. Acta Crystallogr., Sect. E: Struct. Rep. Online 2001, 57, o947−o949. (27) (a) Deagostino, A.; Prandi, C.; Tabasso, S.; Venturello, P. Curr. Org. Chem. 2011, 15, 2390−2412. (b) Westerhausen, M. Dalton Trans. 2006, 4755−4768. (28) (a) Harford, P. J.; Peel, A. J.; Chevallier, F.; Takita, R.; Mongin, F.; Uchiyama, M.; Wheatley, A. E. H. Dalton Trans. 2014, 43, 14181− 14203. (b) Tilly, D.; Chevalier, F.; Mongin, F.; Gros, P. C. Chem. Rev. 2014, 114, 1207−1257. (c) Harrison-Marchand, A.; Mongin, F. Chem. Rev. 2013, 113, 7470−7562. (d) Mongin, F.; Harrison-Marchand, A. Chem. Rev. 2013, 113, 7563−7727. (e) Mulvey, R. E.; Robertson, S. D. Top. Organomet. Chem. 2013, 45, 103−139. (f) Linton, D. J.; Schooler, P.; Wheatley, A. E. H. Coord. Chem. Rev. 2001, 223,53−115. Publication Date (Web): July 7, 2015 | doi: 10.1021/acs.organomet.5b00449 (29) (a) Mulvey, R. E. Dalton Trans. 2013, 42, 6676−6693. (b) Mulvey, R. E. Acc. Chem. Res. 2009, 42, 743−755. (c) Mulvey, R. E.; Mongin, F.; Uchiyama, M.; Kondo, Y. Angew. Chem., Int. Ed. 2007, 46, 3802−3824. (d) Mulvey, R. E. Organometallics 2006, 25,

Downloaded by THURINGER UNIV LANDESBIBLIOTHEK on August 28, 2015 | http://pubs.acs.org 1060−1075. (e) Mulvey, R. E. Chem. Commun. 2001, 1049−1056. (f) Mulvey, R. E. Chem. Soc. Rev. 1998, 27, 339−346. (30) (a) Dagousset, G.; Francois, C.; Leon, T.; Blanc, R.; Sansiaume- Dagousset, E.; Knochel, P. Synthesis 2014, 46, 3133−3171. (b) Klatt, T.; Markiewicz, J. T.; Saemann, C.; Knochel, P. J. Org. Chem. 2014, 79, 4253−4269. (c) Knochel, P.; Barl, N. M.; Werner, V.; Saemann, C. Heterocycles 2014, 88, 827−844. (d) Hevia, E.; Mulvey, R. E. Angew. Chem., Int. Ed. 2011, 50, 6448−6450. (e) Manolikakes, S. M.; Barl, N. M.; Saemann, C.; Knochel, P. Z. Naturforsch., B: J. Chem. Sci. 2013, 68b, 411−422. (f) Knochel, P.; Schade, M. A.; Bernhardt, S.; Manolikakes, G.; Metzger, A.; Piller, F. M.; Rohbogner, C. J.; Mosrin, M. Beilstein J. Org. Chem. 2011, 7, 1261−1277. (g) Haag, B.; Mosrin, M.; Ila, H.; Malakhov, V.; Knochel, P. Angew. Chem., Int. Ed. 2011, 50, 9794−9824. (31) COLLECT, Data Collection Software; Nonius BV, Dordrecht, The Netherlands, 1998. (32) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter, C. W., Sweet, R. M., Eds.; Academic Press: New York, 1997; Vol. 276 (Macromolecular Crystallography, Part A), pp 307−326.

3585 DOI: 10.1021/acs.organomet.5b00449 Organometallics 2015, 34, 3577−3585 Dalton Transactions

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Hydroamination of diphenylbutadiyne with secondary N-methyl-anilines using the dipotassium Cite this: Dalton Trans., 2016, 45, 6241 tetrakis(2,6-diisopropylanilino)calciate precatalyst†

Fadi M. Younis, Sven Krieck, Helmar Görls and Matthias Westerhausen*

The approved precatalyst [K2Ca{N(H)Dipp}4] was employed to study the hydroamination of diphenylbuta- diyne with N-methyl-anilines in tetrahydrofuran at room temperature. The hydroamination occurs regio- selectively within a few hours yielding (N-methyl)-(N-aryl)-1,4-diphenylbut-1-ene-3-yne-1-ylamine with phenyl (1a), 4-tolyl (1b) and 4-fluorophenyl groups (1c). In all cases a mixture of E- and Z-isomers is obtained. The second hydroamination step requires drastically extended reaction times and is successful only for the reaction of diphenylbutadiyne with N-methyl-aniline and N-methyl-4-fluoroaniline giving 1,4-diphenyl-1,4-bis(N-methyl-anilino)buta-1,3-diene [R = H (2a) and F (2c)]; a mixture of E,E-, E,Z- and Received 30th September 2015, Z,Z-isomers is obtained. The X-ray structures of E-1a, E-1b and E-1c show a slightly shortened N–C bond Accepted 18th November 2015 to the alkene moieties. Due to enhanced steric strain the anilino units of Z,Z-2c and Z,Z-3 turn away from DOI: 10.1039/c5dt03818a the butadiene unit and consequently, the lone pair at the planar nitrogen atoms slightly interacts with the www.rsc.org/dalton adjacent aryl groups.

Introduction or alkynes often succeeds in the vicinity of late transition metals.1 Deprotonation of primary and secondary amines and Hydroamination of unsaturated hydrocarbons – the addition formation of amides and imides enhance the reactivity of the of N–H bonds to alkenes and alkynes – represents a highly eli- amines. This method is performed with s-block metals, – gible atom-economical reaction for the synthesis of alkyl- and lanthanoides and early transition metal reagents.2 4 Intra- alkenylamines. However, this reaction is disadvantageous for molecular hydroamination leads to cyclic amines and imines

Published on 20 November 2015. Downloaded by Thueringer Universitats Landesbibliothek Jena 26/04/2016 15:01:54. several reasons. (i) The attack of an electron-rich amine at an and allows the reduction of the disadvantageous entropy electron-rich C–C multiple bond requires to overcome electro- effect. static repulsion. (ii) In addition, this reaction generally is only Very recently the validity of heavier alkaline earth metal very slightly exothermic and, hence, lacks a strong driving reagents in hydroamination reactions has been demonstrated.3 force. (iii) Furthermore, the addition of an amine to an alkene These s-block metals combine the advantageous properties of or alkyne is entropically disfavored due to the reduction of early transition metals (Lewis acidic metal ions, catalytic be- degree of freedom. (iv) The large energy difference between havior, availability of d-orbitals) and typical s-block metals the N–H σ-bond and the C–C π-bond also hampers the facility (strongly heteropolar bonds, high nucleophilicity, electrostatic of this addition reaction. Therefore, several strategies have factors dominate the bonding). In this row calcium represents been developed to overcome the challenges of the hydroami- the most attractive metal because it is globally abundant, avail- nation of unsaturated hydrocarbons. Activation of the alkenes able world-wide, inexpensive, and non-toxic. In order to avoid the entropic challenge, first studies dealt with intramolecular calcium-mediated hydroamination of alkenes.5 The inter-

Institute of Inorganic and Analytical Chemistry, Friedrich-Schiller-University Jena, molecular hydroamination with reagents of the heavier 6 Humboldtstr. 8, D-07743 Jena, Germany. E-mail: [email protected]; http://www. alkaline earth metals required activated alkenes. The inter- lsac1.uni-jena.de; Fax: +49 3641 9-48132 molecular addition of N–H bonds across alkynes seemed to be † Electronic supplementary information (ESI) available: NMR spectra of all new less inhibited.6,7 The hydroamination of diphenylbutadiyne compounds and details of the quantum chemical studies. CCDC 1426897 for proceeded smoothly with N-alkyl-anilines whereas the addition E-1a, 1426898 for E-1b, 1426899 for E-1c, 1426900 for E,E-2a, 1426901 for Z,Z-2c, and 1426902 for Z,Z-3. For ESI and crystallographic data in CIF or other elec- of diphenylamine required a significantly more reactive cata- 7 tronic format see DOI: 10.1039/c5dt03818a lyst system such as the dipotassium calciate [K2Ca(NPh2)4].

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During these calcium-mediated hydroamination reactions only the singly hydroaminated butadiynes were isolated whereas the second CuC triple bond remained intact. A sur- prisingly different behavior was observed for the reaction of primary anilines with diphenylbutadiyne in the presence of a calciate-based catalyst system.8 Depending on the reaction temperature and time either a twofold addition to diphenyl- butadiyne (yielding 2,5-diphenylpyrroles) was observed or a rather complex reaction sequence led to multicyclic com- pounds. In either case, both CuC triple bonds were attacked by N–H functionalities.8 In the latter reaction cascade the substitution pattern of the aniline played a significant role ð1Þ in the constitution of the final product. In all these calcium- We could show earlier8a that also the addition of bulky 2,6- mediated catalytic processes, the calciate [K2Ca{N(H)Dipp}4] diisopropylphenylamine to diphenylbutadiyne can be achieved (Dipp = C6H3-2,6-iPr2) proved to represent an ideal choice because this compound crystallized without ligated ether with [K2Ca{N(H)Dipp}4]. In order to release steric pressure, at bases and consequently, it can be weighed, handled and least one diisopropylanilide anion is exchanged by an stored under an inert atmosphere without aging of the N-methyl-anilide via a transamination reaction forming the ′ crystalline material due to loss of ethereal coligands. In catalytically active species (Scheme 1) yielding LnCa-NRR . L represents Lewis bases such as solvent molecules (thf), amines addition, smaller amines easily replace the bulky Dipp-NH2 – u via transamination reactions in order to release steric or amide anions. The Ca N bond adds to a C C triple bond pressure. leading to intermediate A. The newly formed and very reactive – Based on the finding that anilines react with both CuC Ca C moiety metalates an amine finally yielding E-1 and triple bonds of diphenylbutadiyne we reexamined the hydro- regenerating the catalyst. Even though the E-isomers represent amination of this hydrocarbon with secondary N-methyl- the major product, significant amounts of the Z-isomers are observed. A 1,3-shift of the negative charge leads to the for- anilines of the type HN(Me)(C6H4-4-R) (R = H, Me, F). mation of cumulene B (which might also exist as a solvent-sep- arated ion pair). From this isomer, the back reaction reforms Results and discussion isomer A whereas also the other isomer C can be obtained. Metalation of amine by C yields Z-1. Singly hydroaminated diphenylbutadiyne In these studies we used again the approved catalyst and varied the amine. The use of secondary amines guarantees that the rather complex cyclization reactions are suppressed. N-Methyl-anilines were reacted with diphenylbutadiyne in the

presence of catalytic amounts of [K2Ca{N(H)Dipp}4]. In a

Published on 20 November 2015. Downloaded by Thueringer Universitats Landesbibliothek Jena 26/04/2016 15:01:54. standard procedure, diphenylbutadiyne was dissolved in tetrahydrofuran (THF). At room temperature, an equimolar

amount of N-methyl-aniline HN(Me)C6H4-4-R (R = H, Me, F) and 5 mol% of the catalyst were added. This solution was stirred for several hours at room temperature. Repeated NMR measurements showed the conversion of the amine and the formation of singly hydroaminated diphenylbutadiynes (R = H[1a], Me [1b], F [1c]) as a mixture of E- and Z-isomers according to eqn (1). After quantitative conversion the reac- tion mixture was hydrolyzed with distilled water. The aqueous solution was extracted with diethyl ether. The ether fractions were combined, dried with sodium sulfate and then the ether was removed yielding E/Z-isomer mixtures of the tertiary amines 1-(N-methyl-anilino)-1,4-diphenylbut-1-ene-3- yne with E/Z ratios of approximately 1 : 0.6 (1a), 1 : 1 (1b) and 1 : 0.9 (1c). Recrystallization from a solvent mixture of Scheme 1 Proposed catalytic cycle for the calcium-mediated hydro- ’ dichloromethane and pentane gave pure compounds; amination of diphenylbutadiyne (Ph = phenyl; R,R = methyl, aryl). Due to the fact that the exact composition of the catalytic species is however, the different isomers exhibited rather similar solu- unknown, the calcium catalyst is shown as [LnCaNRR’] with L represent- bility properties hampering a fractional crystallization under ing any Lewis base such as thf (solvent), amines and amides such as the these conditions. anions NRR’− and N(H)Dipp−.

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Table 1 Selected structural parameters (bond lengths [pm] and angles [°]) of the E-isomers E-1a, E-1b, and E-1c

E-1a E-1b E-1c

N1–C17 146.78(16) 146.78(18) 146.76(13) N1–C18 143.17(16) 143.10(17) 143.19(13) N1–C1 139.99(15) 139.94(17) 139.97(13) C1–C11 148.74(17) 149.09(18) 149.18(14) C1–C2 135.33(17) 135.53(19) 135.77(15) C2–C3 142.34(17) 142.29(19) 142.37(15) C3–C4 120.27(18) 120.31(19) 120.40(15) C4–C5 143.39(17) 143.38(19) 143.61(14) C17–N1–C18 115.11(10) 115.06(11) 114.81(8) C1–N1–C17 117.79(10) 117.88(11) 117.92(9) C1–N1–C18 117.95(10) 119.37(11) 118.38(8) – – Fig. 1 Molecular structure and numbering scheme of E-1c. The ellip- N1 C1 C2 122.06(11) 121.07(12) 121.68(9) N1–C1–C11 115.49(10) 115.49(11) 115.75(9) soids represent a probability of 30%, H atoms are drawn with arbitrary C2–C1–C11 122.21(11) 123.22(12) 122.38(9) radii. Selected structural parameters are listed in Table 1. C1–C2–C3 125.01(12) 126.78(13) 125.86(10) C2–C3–C4 176.09(13) 173.87(14) 175.45(11) C3–C4–C5 176.23(13) 177.59(14) 177.34(11)

The molecular structure and numbering scheme of E-(1,4- diphenylbut-1-ene-3-yne-1-yl)-(4-fluorophenyl)-methylamine (E-1c) is depicted in Fig. 1. The essential structural parameters three days an E/Z-isomeric mixture of 1,4-di(N-methyl- of E-1a, E-1b, and E-1c are very similar and summarized in anilino)-1,4-diphenylbuta-1,3-diene (2a) according to eqn (2). Table 1. The nitrogen atom N1 is in a nearly planar environ- Again, the conversion was controlled by NMR spectroscopy ment allowing conjugation of the lone pair with the but-1-ene- measurements as depicted in Fig. 2. These NMR studies 3-yne unit. The N1–C17 and N1–C18 bond lengths represent showed that the formation of the E-isomer is favored but 3 2 characteristic N–C values to sp and sp hybridized carbon again cis- and trans-addition was observed for the second atoms, respectively. The shorter N1–C1 bond lengths hint hydroamination step, yielding E,Z- and E,E-1,4-di(N-methyl- toward a slight conjugation with the alkene moieties. The anilino)-1,4-diphenylbuta-1,3-diene as the major components. π-system of the alkene fragments do not interact with the adja- The E,E- and Z,Z-isomers form with a ratio of 3 : 1. This is cent phenyl group. The C1vC2 bond (135.3 to 135.8 pm) is in agreement with the formation of the singly hydroami- only slightly elongated compared to the expected value of a nated compounds E-1a and Z-1a where the E-isomer also 2 double bond between the sp hybridized carbon atoms (134 represents the favored product. A complete conversion was 9 pm). The C3uC4 bond reflects the characteristic value of an not achieved under these reaction conditions. A final NMR isolated triple bond. experiment after approx. one month still contained singly Selected NMR data are summarized in Table 2. The num- hydroaminated 1a. bering scheme for the carbon atoms is identical to the num- The yields of doubly hydroamination products 2a and 2c

Published on 20 November 2015. Downloaded by Thueringer Universitats Landesbibliothek Jena 26/04/2016 15:01:54. bering of the X-ray structures discussed above. For the were determined approx. after one month (eqn (2)) with minor assignment, single crystals of the E-isomers were dissolved in amounts of the mono-hydroamination products 1a and 1c, an appropriate solvent and NMR experiments (H,H-COSY, respectively, still present. The ratio of the isomers of 2a was HMBC and HSQC spectra) allowed an unambiguous assign- determined by the integration of the 1H NMR spectrum. For 2c ment of these resonances. The NMR signals of the aryl groups one major component was observed in the NMR spectra are listed in the Experimental section, an assignment to accompanied by resonances of very weak intensity (see the specific carbon atoms was not possible. Thereafter, a mixture ESI†); therefore a reliable assignment was not possible in the of both isomers allowed us to also assign the resonances of 1H NMR spectrum. the Z-isomers. The time-dependent conversion of the singly hydroaminated The hydrogen atoms at the C2 atoms clearly allow us to dis- diphenylbutadiyne 1a to the doubly hydroaminated derivative tinguish between the E- and Z-isomer because the resonances 2a is depicted in Fig. 3. The s-block metal-mediated hydroami- of the E-isomers are shifted toward a lower field by approx. nation of the second CC triple bond of diphenylbutadiyne is sig- 0.5 ppm. A comparable effect, albeit smaller, is also observed nificantly slower than the first hydroamination process, 13 1 for the N-bound methyl groups. In the C{ H} NMR spectra allowing the isolation of pure mono-hydroamination product only small differences of the chemical shifts of the isomers 1a. However, a mono-hydroaminated product was still present can be found. after several days and weeks. Thus, the reaction solution showed a mixture of 10% of Z-1a and 20% of E-1a as well as Doubly hydroaminated diphenylbutadiyne 30% of E,E-2a,30%ofE,Z-2a and 10% of Z,Z-2a after 72 hours. The reaction of diphenylbutadiyne with a twofold stoichio- The bulkier N-methyl-p-toluidine (R = Me) reacted only once metric amount of N-methyl-aniline (R = H) yielded after regardless of the applied stoichiometry giving exclusively the

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ð2Þ

singly hydroaminated product 1b. In contrast to this inhibition stituted phenyl groups. In Fig. 6, the C–F and C–H bonds to by a para-methyl substituent, the hydroamination of diphenyl- the disordered atoms with occupancy factors of 50% are butadiyne with N-methyl-para-fluoroaniline (R = F) showed shown as broken lines; only one orientation of this molecule is that the second hydroamination step also occurred readily depicted. Due to the fact that the influence of the para-posi- leading to E/Z-mixtures of 1,4-di(N-methyl-para-fluoroanilino)- tioned substituents on the structure of the central moieties is 1,4-diphenylbuta-1,3-diene (2c). The reaction of 1-(N-methyl- negligible in the singly hydroaminated derivatives 1, the struc- anilino)-1,4-diphenylbut-1-ene-3-yne (1a) with N-methyl-para- tural parameters are reliable and are included in our discus- fluoroaniline led to the formation of the asymmetric 1,4-hydro- sions. Selected structural data are summarized in Table 3. aminated butadiene derivative 3. Due to the lack of formation The central butadiene units resemble characteristic bond of symmetric 2a and 2c equilibrium with amination–deamina- lengths of C–C single and CvC double bonds without signifi- tion pathways can be excluded. In contrast to these findings cant charge delocalization. In agreement with this interpret- N-methyl-toluidine again showed no tendency to react with ation, the C1–C10 bond lengths to the phenyl groups resemble the second CuC triple bond of 1a under these reaction characteristic single bond values between sp2 hybridized conditions. carbon atoms.9 Due to the crystallographic inversion symmetry The centrosymmetric molecular structures of the doubly the buta-1,3-diene units are strictly planar. According to the hydroaminated isomers E,E-2a and Z,Z-2c are displayed in VSEPR concept multiple bonds are more demanding than Fig. 4 and 5. The asymmetric derivative 3 crystallized as a Z,Z- single bonds and therefore, they require more space leading to

isomer in the centrosymmetric monoclinic space group P21/c decreased N1–C1–C11 bond angles. with the center of symmetry on the butadiene unit leading to In the E-isomeric mono-hydroamination products 1a to 1c, Published on 20 November 2015. Downloaded by Thueringer Universitats Landesbibliothek Jena 26/04/2016 15:01:54. 1 : 1 disordering of the 4-fluorophenyl and the N-bound unsub- the N–C bond to the butadiene fragment is shorter than the

Table 2 Selected NMR data of the singly hydroaminated diphenylbutadiyne. The numbering scheme is identical to the molecular structures and can be seen in Fig. 1

E-1a E-1a Z-1a E-1b Z-1b E-1c Z-1c

Solvent DMSO [D8]THF [D8]THF [D8]THF [D8]THF CD2Cl2 CD2Cl2 1H C2–H 5.96 5.83 5.28 5.69 5.17 5.75 5.21 C17–H 3.34 3.40 3.25 3.42 3.26 3.40 3.23

13C{1H} C1 155.1 155.9 158.2 156.2 158.2 157.9 160.5 C2 99.9 100.3 90.6 88.8 87.5 88.3 88.9 C3 97.4 98.4 90.8a 90.6a 90.9a 99.1 97.9 C4 88.3 88.6 91.1a 91.1a 90.1a 90.5 90.4 C11 137.6 139.3 137.7 139.6 137.2 137.1 138.8 C17 39.4 39.5 41.5 40.0 42.2 41.6 39.7 C18 147.0 148.3 149.2 146.7 146.1 144.6 145.1

a Assignment uncertain.

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Dalton Transactions Paper

Fig. 2 NMR spectroscopic monitoring of the second hydroamination of

an E/Z-mixture of 1a in the presence of catalytic amounts of [K2Ca{N(H)- Dipp}4] (400 MHz, r.t., [D8]THF). The progress of the second hydroami- nation step can be elucidated from the resonances of the butadiene Fig. 4 Molecular structure and numbering scheme of centrosymmetric E E “ ” units in the region between δ = 5.3 and 7.0 ppm. The spectra were , -2a. Symmetry-related atoms are marked with the letter A . The recorded after 1 h, 5 h, 21 h, 29 h, 59 h, and 72 h (from bottom to top) ellipsoids represent a probability of 30%, H atoms are shown with arbi- after mixing of the substrates. In the bottom spectrum E-1a (δ = trary radii. Selected structural parameters are listed in Table 3. 5.82 ppm) and Z-1a (δ = 5.28 ppm) are the major components; after 72 h, these compounds together with the doubly hydroaminated diphe- nylbutadiynes E,E-2a (δ = 6.59 ppm), E,Z-2a (δ = 5.93 and 6.7 ppm), and Z,Z-2a (δ = 6.26 ppm) are observed. Published on 20 November 2015. Downloaded by Thueringer Universitats Landesbibliothek Jena 26/04/2016 15:01:54.

Fig. 5 Molecular structure and numbering scheme of centrosymmetric Z,Z-2c. Symmetry-related atoms are marked with the letter “A”. The Fig. 3 Time-dependent conversion of the singly hydroaminated com- ellipsoids represent a probability of 30%, H atoms are drawn with arbi- pounds E-1a and Z-1a to the doubly hydroaminated isomer mixture 2a trary radii. Selected bond lengths and angles are summarized in Table 3. in the presence of 5 mol% of catalytically active [K2Ca{N(H)Dipp}4]in THF at room temperature. Due to the fact that no side-products formed during this s-block metal-mediated hydroamination all compounds add up to 100%. cent aryl group resembles a slight interaction between the lone pair at N1 and the π-system of this aryl group. In E,E-isomeric 2a the N1–C1 and N1–C4 bond lengths show very similar bond to the aryl group. This trend is also realized in the values with a smaller degree of charge delocalization. This doubly hydroaminated E,E-isomeric derivative. In the Z,Z- finding verifies that the direction of the small contributions of isomers 2c and 3 a characteristic N1–C1 single bond is π-interaction is dictated by the minimization of steric pressure observed whereas a shortening of the N1–C4 bond to the adja- within the molecules.

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The second hydroamination step of the other CuC triple bond requires much longer time under similar reaction con- ditions. After three days mixtures of singly and doubly hydroaminated diphenylbutadiyne were obtained when N-methylaniline and N-methyl-4-fluoroaniline were employed. In contrast to this finding, no significant amount of doubly hydroaminated diphenylbutadiyne was observed in the NMR spectra for the hydroamination with N-methyl-4-tolylamine. Again, the catalytic hydroamination gave regioselectively 1,4- diphenyl-1,4-bis(N-methylanilino)buta-1,3-diene [R = H (2a) and F (2c)] but a mixture of E,E-, E,Z- and Z,Z-stereoisomers was obtained. The extremely decelerated second hydroamina- tion allowed the isolation of pure singly hydroaminated diphenylbutadiyne. The catalytic hydroamination of 1a with N-methyl-4-fluoroaniline yielded exclusively the mixed doubly hydroaminated product 3 as a stereoisomeric mixture. The Fig. 6 Molecular structure and numbering scheme of Z,Z-3. Sym- absence of 2a and 2c verifies that amination–deamination metry-related atoms are marked with the letter “A”. Due to the centro- equilibrium can be excluded. fl symmetry the uorine and hydrogen atoms at C7 (the respective bonds The X-ray structures of E-isomeric 1 suggest that the lone are depicted as broken lines) is disordered with a 1 : 1 ratio, only one pair of the nitrogen atoms show only a very small interaction orientation is depicted in this figure (see text). The ellipsoids represent a π v probability of 30%, H atoms are shown with arbitrary radii. with the -systems of the adjacent C C double bonds whereas no delocalization into the N-bound aryl groups can be substan- tiated. The second amino group enhances steric strain and in Z,Z-isomeric 2c and 3 the lone pairs of the nitrogen atoms slightly interact with the π-systems of the N-bound aryl groups. Table 3 Selected structural parameters (bond lengths [pm] and angles This observation suggests that steric reasons might account [°]) of the doubly hydroaminated diphenylbutadiyne for the significantly slower second hydroamination step. E,E-2a Z,Z-2c Z,Z-3

N1–C4 141.9(3) 139.5(3) 139.2(3) N1–C3 146.2(3) 146.0(3) 145.7(3) Experimental N1–C1 141.4(3) 143.1(3) 142.9(2) C1–C10 148.3(4) 147.7(4) 148.1(3) General remarks – C1 C2 136.0(4) 135.1(4) 135.1(3) All manipulations were carried out under an inert nitrogen C2–C2A 143.8(5) 143.8(5) 144.3(4) C3–N1–C4 116.9(2) 119.0(2) 119.8(2) atmosphere using standard Schlenk techniques. The solvent C1–N1–C3 117.6(2) 117.0(2) 118.6(2) was dried over KOH and subsequently distilled over sodium/ – – C1 N1 C4 120.8(2) 121.5(2) 121.5(2) benzophenone under a nitrogen atmosphere prior to use. C2–C1–C10 123.8(2) 122.0(2) 122.4(2) Published on 20 November 2015. Downloaded by Thueringer Universitats Landesbibliothek Jena 26/04/2016 15:01:54. N1–C1–C10 115.1(2) 117.2(2) 117.5(2) Deuterated solvents were dried over sodium, degassed, and N1–C1–C2 121.1(2) 120.8(2) 119.8(2) saturated with nitrogen. The yields given are not optimized. – – C1 C2 C2a 126.6(3) 125.5(3) 125.0(2) 1H and 13C{1H} NMR spectra were recorded on Bruker AC 400 and AC 600 spectrometers. Chemical shifts are reported in

parts per million relative to SiMe4 as an external standard. The residual signals of the deuterated solvents [D8]THF and CD2Cl2 Conclusion were used as internal standards. The solvent-free and recrystal- lized precatalyst [K2Ca{N(H)Dipp}4] was prepared according to 8 The proven precatalyst [K2Ca{N(H)Dipp}4] was employed to a literature procedure. A specific amount of this compound study the hydroamination of diphenylbutadiyne with second- was dissolved in anhydrous THF and aliquots of this solution ary N-methyl-anilines in tetrahydrofuran at room temperature. were added to the reaction mixtures. This procedure allowed After approximately 6 h a nearly complete conversion with a us to easily add definite amounts of the precatalyst to the sub- catalyst loading of 5 mol% led to singly hydroaminated buta- strates under strictly anaerobic conditions. All substrates were diyne. Diverse para-substituents such as H, Me and F were purchased from Sigma Aldrich, Merck or Alfa Aesar and used tested and yielded the desired hydroamination products (N- without further purification. The isomeric ratios are discussed methyl)-(N-aryl)-1,4-diphenylbut-1-ene-3-yne-1-ylamine of the in the text and are given underneath the reaction equations. type [Ph–CuC–CHv(Ph)C]N(Me)(C6H4-4-R) with R = H (1a), (N-Methyl)-1,4-diphenylbut-1-ene-3-yne-1-ylaniline (1a). To a Me (1b) and F (1c). This hydroamination was regioselective; solution of diphenylbutadiyne (0.25 g, 1.23 mmol) in 20 ml of however, both stereoisomers with E- and Z-arrangements at THF, N-methylaniline (0.13 g, 1.23 mmol) and 5 mol% of the v the C C double bond were formed. calciate precatalyst [K2Ca{N(H)Dipp}4] were added and stirred

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Dalton Transactions Paper

for 6 hours at r.t. A standard workup procedure including C2H, E), 3.42 (s, 3H, C17H, Z), 3.22 (s, 3H, C17H, E), 2.19 (s, hydrolysis with 17 ml of distilled water, extraction with diethyl 3H, C24H, Z), 2.18 (s, 3H, C24H, E). 13C{1H} NMR (151 MHz,

ether, drying with sodium sulfate and recrystallization in thf-d8) δ 158.5 (C1, E), 156.2 (C1, Z), 146.7 (C18, E), 146.1 (C18, pentane at 5 °C yielded colorless crystals from a yellow mother Z), 139.6 (C11, Z), 137.8 (C11, E), 133.3, 131.7, 131, 130.9, liquor (0.35 g, 1.13 mmol, 92%). M.p. 118 °C. Elemental analy- 129.7, 129.3, 129.1, 128.9, 128.8, 128.7, 128.7, 128.2, 128.1,

sis (C23H19N, 309.39): calc.: C 89.28, H 6.19, N 4.53; found: 127.2, 126.1, 125.1, 124.9, 118.1, 98.7 (C2, E), 98 (C3, E), 91.1 C 88.84, H 6.26, N 4.47. MS [EI, m/z (%)]: 309 (90) [M], 202 (15) (C4, Z), 90.6 (C3, Z), 89 (C4, E), 88.8 (C2, Z), 41.8 (C17, E), 40

[diyne], 146 (15), 118 (100) [PhNC2H3], 91 (10) [N-Ph], 77 (45) (C17, Z), 20.6 (C24, E), 20.4 (C24, Z). [Ph]. IR 3078 w, 3055 w, 3032 w, 2998.54 w, 2958 w, 2889 w, (N-Methyl)-(N-4-fluorophenyl)-1,4-diphenylbut-1-ene-3-yne-1- 2815 w, 2188 w, 1596 s, 1578 s, 1560 w, 1549 w, 1487 s, ylamine (1c). To a solution of diphenylbutadiyne (0.15 g 1471 m, 1422 w, 1385 m, 1095 m, 1026 m, 1007 m, 917 m, 0.74 mmol) in THF (12 ml), 4-fluoro-N-methylaniline (0.092 g,

751 vs, 694 vs, 588 w, 521 m, 493 m, 407 w. 0.74 mmol) and 5 mol% of the calciate catalyst [K2Ca{N(H)- 1 E-Isomer: H NMR (400 MHz, DMSO): δ 7.46 (m, 2H, Ar–H), Dipp}4] were added and stirred for six hours at r.t. A standard 7.36 (m, 3H, Ar–H), 7.30 (m, 3H, Ar–H), 7.15 (m, 4H, Ar–H), workup procedure including hydrolysis with 10 ml of distilled 3 3 6.78 (d, JH,H = 8.1 Hz, 2H,), 6.72 (t, JH,H = 7.2 Hz, 1H, C21H), water, extraction with diethyl ether, drying with sodium sulfate 5.96 (s, 1H, C2H), 3.34 (s, 3H, C17H). 13C{1H} NMR (DMSO, and recrystallization in the diffusion method (dichloro- E-isomer): δ 155.1 (C1), 147.0 (C18), 137.61 (C11), 130.9, 129.2, methane/pentane) at 5 °C yields colorless crystals in yellow 128.8, 128.7, 128.6, 128.3, 127, 123.1, 118.6, 116.1, 99.9 (C2), solution (0.190 g 0.58 mmol, 78%). M.p. 121 °C. Elemental

97.4 (C3), 88.3 (C4), 39.4 (C17). analysis (C30H27N2F, 434.22): calc.: C 84.38, H 5.54, N 4.28, F Mixture of E- and Z-isomers (approx. 6 : 4): 1H NMR 5.80; found: C 84.12, H 5.58, N 4.45. MS [EI, m/z (%)]: 327 3 (400 MHz, [D8]THF): δ 7.60 (d, JH,H = 7.1 Hz, Ar–H), 7.47 (m, (100) [M], 202 (50) [diyne], 189 (30), 118 (100) [PhNC2H3], 95

Ar–H), 7.19 (m, Ar–H), 7.01 (d, J = 7.8 Hz, Ar–H), 6.85 (d, JH,H = (60), 77 (90) [Ph]. IR: 3052 w, 3028 w, 2919 w, 2849 w, 2184 w, 8.2 Hz, Ar–H), 6.71 (t, J = 7.3 Hz, Ar–H), 5.83 (s, C2H, E), 5.28 1580 w, 1560 m, 1504 s, 1486 s, 1469 m, 1441 m, 1360 m, 13 1 (s, C2H, Z), 3.40 (s, H3, E), 3.25 (s, CH3, Z). C{ H} NMR 1486 m, 1222 s, 1108 m, 1023 w, 915 m, 795 s, 754 s, 688 s,

(101 MHz, [D8]THF): δ 158.2 (C1, Z), 155.9 (C1, E), 149.2 (C18, 535 m, 524 m, 523 m, 487 m, 474 w, 428 w. E Z 1 Z), 148.3 (C18, E), 139.3 (C11, E), 137.7 (C11, Z), 131.8, 131.1, Mixture of - and -isomers: H NMR (400 MHz, [D8]THF): 130.8, 129.5, 129.3, 129.2, 129.1, 128.9, 128.7, 128.3, 128.2, δ 7.59–7.54 (m, Ar–H), 7.48–7.42 (m, Ar–H), 7.33–7.09 (m, Ar– 127.9, 127.3, 125.9, 124.9, 124.3, 123.4, 119.4, 117.2, 100.3 (C2, H), 7.04–6.98 (m, Ar–H), 6.92–6.81 (m, Ar–H), 5.75 (s, C2H, E), 13 1 E), 98.4(C3, E), 91.1 (C4, Z), 90.8 (C3, Z), 90.6 (C2, Z), 88.6 (C4, 5.21 (s, C2H, Z), 3.40 (s, CH3, E), 3.23 (s, CH3, Z). C{ H} NMR 1 E), 41.5 (C17, E), 39.5 (C17, E). (101 MHz, [D8]THF): δ 160.5 (C1, Z), 158.3 (d, JC,F = 24.3 Hz), 4 (N-Methyl)-(N-4-tolyl)-1,4-diphenylbut-1-ene-3-yne-1-ylamine 157.9 (C1, E), 156.1 (C22, Z), 155.6 (C22, E), 145.13 (d, JC,F = 4 (1b). To a solution of diphenylbutadiyne (0.25 g, 1.23 mmol) 2.6 Hz, C18, Z), 144.56 (d, JC,F = 2.1 Hz, C18, E), 138.8 (C11, in THF (17 ml), N-methyl-p-toluidine (0.149 g, 1.23 mmol) and Z), 137.1, 132, 131.3, 130.7, 130.5, 129.2, 128.8, 128.6, 128.5,

5 mol% of the calciate [K2Ca{N(H)Dipp}4] were added and 128.4, 128, 127.8, 127.6, 127, 126.4, 126.3, 125.6, 124.5, 122.5, stirred for 7 hours at r.t. Hydrolysis with 15 ml of distilled 118.5, 118.5, 117.7, 115.7, 115.5, 115.3, 115.1, 99.1, 97.9, 90.5, water, extraction with diethyl ether, drying with sodium sulfate 90.4, 88.9, 88.3, 41.6 (C17, E), 39.7 (C17, Z). 19F NMR

Published on 20 November 2015. Downloaded by Thueringer Universitats Landesbibliothek Jena 26/04/2016 15:01:54. and recrystallization in pentane at 5 °C yielded colorless crys- (188 MHz, THF): δ −123 (Z), −129.2 (E). tals in a yellow mother liquor (0.35 g, 1.08 mmol, 88%). 1,4-Diphenyl-1,4-bis(N-methylanilino)buta-1,3-diene (2a).

M.p. 120 °C. Elemental analysis (C24H21N, 323.42): calc.: C 89.12, Diphenylbutadiyne (0.25 g, 1.23 mmol) was dissolved in 17 ml H 6.54, N 4.33; found: C 88.86, H 6.64, N 4.49. MS [EI, m/z of THF before N-methylaniline (0.26 g, 2.47 mmol) and 5 mol

(%)]: 323 (100) [M], 202 (15) [Ph2C4], 146 (15), 118 (100) % of calciate [K2Ca{N(H)Dipp}4] were added and stirred for [PhNC2H3], 91 (10) [N-Ph], 77 (20) [Ph], 43 (60). IR: 3064 w, three days at r.t. The standard workup procedure included 3030 w, 2899 w, 2876 w, 2857 w, 2821 w, 2186 w, 2170 w, 1598 s, hydrolysis with 15 ml of distilled water, extraction with diethyl 1565 m, 1513 s, 1549 w, 1486 m, 1469 m, 1444 m, 1360 s, ether, drying with sodium sulfate and fractional recrystalliza- 1105 s, 801 s, 762 s, 749 s, 704 s, 693 s, 523 m, 521 m, 503 m, tion from dichloromethane and pentane at 5 °C yielding 0.45 g 485 m, 474 w. of colorless crystals from a yellow solution. The crystal fraction E 1 δ – 1 -Isomer: H NMR (400 MHz, CD2Cl2): 7.65 6.83 contained also minor amounts of 1a. M.p. 121 °C. H NMR (m, 14H), 5.17 (s, 1H, C2H), 3.26 (s, 3H, C17H), 2.22 (s, 3H, (600 MHz, CD2Cl2): δ 7.62 (d, J = 7.2 Hz, Ar–H), 7.48 (m, Ar–H), 13 C24H). C NMR (101 MHz, CD2Cl2) δ 158.2 (C1, E), 146.1 7.42 (d, JH,H = 7.7 Hz, Ar–H), 7.38–7.30 (m, Ar–H), 7.31–7.24 – – – – – (C18, E), 137.2(C11, E), 133.5, 130.7, 130.5, 129.7, 128.6, 128.5, (m, Ar H), 7.25 7.21 (m, Ar H), 7.21 7.12 (m, Ar H), 7.09 (t, JH, 127.9, 127.1, 125.2, 124.9, 90.9 (C3, E), 90.1 (C4, E), 87.5 H = 7.9 Hz, Ar–H), 7.02 (d, J = 7.8 Hz, Ar–H), 6.96–6.90 (m, Ar–

(C2, E), 42.2 (C17, E), 20.8 (C24, E). H), 6.89 (d, JH,H = 8.2 Hz, Ar–H), 6.84–6.75 (m, Ar–H), 6.72 (m, E Z 1 – – – – Mixture of - and -isomers (1 : 1): H NMR (600 MHz, thf- Ar H), 6.70 6.65 (m, Ar H), 6.61 (d, JH,H = 8.1 Hz, Ar H), 6.59 3 d8): δ 7.60–7.54 (m, 2H, Ar–H, E,Z), 7.44 (m, 2H, Ar–H, E,Z), (s, C2H, C2AH, Z–Z), 6.24 (s, C2H, C2AH, E–E), 5.94 (d, JH,H = 7.32–7.08 (m, 16H, Ar–H, E,Z), 6.92 (m, 6H, Ar–H, E,Z), 11.3 Hz, C2H, C2AH, E–Z, Z–E), 5.79 (s, C2H, E), 5.28 (s, C2H, – – – 6.81 6.72 (m, 2H, Ar H, E,Z), 5.69 (s, 1H, C2H, Z), 5.18 (s, 1H, Z), 3.43 (s, C17H3, E), 3.30 (s, C17H3, Z), 3.24 (s, CH3, E E),

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13 3.13 (s, CH3, Z–Z), 3.11 (s, CH3, E–Z, Z–E). C NMR (151 MHz, 113.9, 113.1, 112.6, 110.6, 99.9 (C2, E), 97.9 (C3, E) 90.62 (C2, δ CD2Cl2): 157. (C1, Z), 155.6(C1, E), 150.51 (C18, Z), 149.37 Z), 89.3 (C2, C3, Z), 88.3 (C4, E), 41.9 (C17, Z), 41.4 (C3,C3A, (C18, E), 148.9, 148.8, 148.7, 148.6, 147.9, 146, 145.4, 139.6, Z–Z), 40.4 (C3,C3A, Z–E, E–Z), 39.7 (C17-E), 39.2 (C3, E,E).

139.1, 138.8, 138.6, 138.1, 137.8, 137.1, 131.4, 130.8, 130.7, Elemental analysis (C30H28N2, 323.42): calc.: C 86.50, H 6.78, 130.5, 130.1, 129.3, 129.3, 129.1, 128.9, 128.9, 128.9, 128.9, N 6.72; found: C 86.52, H 6.48, N 7.00. MS [EI, m/z (%)]: 417 (23) 128.8, 128.7, 128.7, 128.5, 128.4, 128.4, 128.2, 128, 127.6, [M+], 417 (78) [M], 309 (95) [M − L], 202 (35) [diyne], 118 (90)

127.2, 127.1, 127, 125.9, 125.1, 124.4, 124.1, 123.8, 123.3, [PhNC2H3], 91 (35) [N-Ph], 77 (100) [Ph]. IR 3027 w, 2962 w, 122.7, 122, 121.1, 119.7, 119.2, 119.1, 117.6, 117, 116.8, 116.8, 2901 w, 2189 w, 1598 s, 1580 s, 1561 vs, 1487 m, 1471 s, 1445 s,

Table 4 Crystal data and refinement details for the X-ray structure determinations of compounds 1a–1c and 2a–3

Compound E-1a E-1b E-1c

Formula C23H19NC24H21NC23H18FN −1 fw (g mol ) 309.39 323.42 327.38 T/°C −140(2) −140(2) −140(2) Crystal system Monoclinic Monoclinic Monoclinic Space group P21/cP21/cP21/c a/Å 7.2645(2) 7.4316(1) 7.2846(1) b/Å 22.7706(5) 23.6631(7) 23.2679(5) c/Å 10.5374(2) 10.6845(3) 10.5794(2) α/° 90 90 90 β/° 97.257(1) 100.375(2) 98.835(1) γ/° 90 90 90 V/Å3 1729.10(7) 1848.20(8) 1771.90(6) Z 444 − ρ (g cm 3) 1.188 1.162 1.227 − μ (cm 1) 0.68 0.67 0.78 Measured data 11 309 10 544 12 883 Data with I >2σ(I) 3367 3444 3744 Unique data (Rint) 3947/0.0301 4224/0.0313 4032/0.0211 2 a wR2 (all data, on F ) 0.0996 0.1079 0.0912 a R1 (I >2σ(I)) 0.0432 0.0468 0.0385 Sb 1.064 1.069 1.048 − Res. dens./e Å 3 0.195/−0.166 0.263/−0.183 0.234/−0.183 Absorpt method Multi-scan Multi-scan Multi-scan Absorpt corr Tmin/max 0.6322/0.7456 0.6553/0.7456 0.7006/0.7456 CCDC no. 1426897 1426898 1426899

Compound E,E-2a Z,Z-2c Z,Z-3

Formula C30H28N2 C30H26F2N2 C30H27FN2 −1 fw (g mol ) 416.54 452.53 434.54

Published on 20 November 2015. Downloaded by Thueringer Universitats Landesbibliothek Jena 26/04/2016 15:01:54. T/°C −140(2) −140(2) −140(2) Crystal system Monoclinic Monoclinic Monoclinic Space group P21/nP21/cP21/c a/Å 10.5309(15) 11.0689(3) 11.7393(4) b/Å 11.255(2) 12.6418(4) 8.3583(3) c/Å 10.6349(17) 8.3768(2) 11.9106(4) α/° 90 90 90 β/° 113.94(1) 102.224(2) 100.576(2) γ/° 90.00 90 90 V/Å3 1152.1(3) 1145.60(6) 1148.82(7) Z 222 − ρ (g cm 3) 1.201 1.312 1.256 − μ (cm 1) 0.7 0.88 0.79 Measured data 7660 6189 7762 Data with I >2σ(I) 1700 1963 2346 Unique data (Rint) 2507/0.0594 2173/0.0364 2618/0.0360 2 a wR2 (all data, on F ) 0.1796 0.1838 0.1824 σ a R1 (I >2 (I)) 0.0791 0.0648 0.0671 Sb 1.135 1.153 1.159 − Res. dens./e Å 3 0.214/−0.309 0.295/−0.241 0.378/−0.241 Absorpt method Multi-scan Multi-scan Multi-scan Absorpt corr Tmin/max 0.5072/0.7456 0.5222/0.7456 0.6842/0.7456 CCDC no. 1426900 1426901 1426902

a ∑ − ∑ ∑ 2 − 2 2 ∑ 2 2 1/2 −1 σ2 2 2 2 2 Definition of the R indices: R1 =( ||Fo| |Fc||)/ |Fo|; wR2 ={ [w(Fo Fc ) ]/ [w(Fo ) ]} with w = (Fo )+(aP) + bP; P =[2Fc +max(Fo )]/3. b ∑ 2 − 2 2 − 1/2 s ={ [w(Fo Fc ) ]/(No Np)} .

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Dalton Transactions Paper

1363 m, 1335 w, 1305 w, 1260 m, 1237 m, 1189 m, 1106 s, 1028 mated Mo-Kα radiation. Data were corrected for Lorentz and s, 766 m, 746 vs, 720 vs, 690 vs, 682 vs, 524 m, 499 m, 407 w. polarization effects; absorption was taken into account on a – 1,4-Diphenyl-1,4-bis(N-methyl-4-fluoroanilino)buta-1,3-diene semi-empirical basis using multiple-scans.10 12 The structure (2c). To a solution of diphenylbutadiyne (0.1 g, 0.49 mmol) in was solved by direct methods (SHELXS)13 and refined by full- 2 13 12 ml of THF, N-methyl-4-fluoroaniline (0.12 g, 0.115 ml, matrix least squares techniques against Fo (SHELXL-97). All 0.10 mmol) and 5 mol% of [K2Ca{N(H)Dipp}4] were added and non-disordered hydrogen atoms were located by difference stirred for three days at r.t. Hydrolysis with 15 ml of distilled Fourier synthesis and refined isotropically. All non-hydrogen water, extraction with diethyl ether, drying with sodium sulfate atoms were refined anisotropically.13 Crystallographic data as and recrystallization from dichloromethane and pentane at well as structure solution and refinement details are summar- 5 °C yielded colorless crystals in a yellow mother liquor ized in Table 4. The programs XP (SIEMENS Analytical X-ray (0.20 g, 0.44 mmol, 90%). M.p. 196–201 °C. 1H NMR Instruments, Inc.)14 and POV-Ray15 were used for structure

(400 MHz, CD2Cl2): δ 7.29–7.21 (m, 10H, Ar–H), 6.95–6.84 (m, representations. 4H, Ar–H), 6.74–6.66 (m, 4H, Ar–H), 6.52 (s, 2H, C1H, C1AH), 13 1 3.26 (s, 6H, C9, C9A, CH3). C{ H} NMR (101 MHz, CD2Cl2): 1 δ 156.1 (d, JC,F = 235.0 Hz, C13, C13A), 146.1 (C2,C2A), 145.35 4 Acknowledgements (d, JC,F = 1.8 Hz C10,C10A), 138.5 (C3,C3A), 128.9, 128.5, 127, 120.7, 115.7, 115.5, 114.7, 40 (C9, C9A). 19F NMR (188 MHz, We appreciate the financial support of the Fonds der Che-

CD2Cl2): δ −129.5. Elemental analysis (C30H26N2F2, 452.53): mischen Industrie im Verband der Chemischen Industrie e.V. calc.: C 79.62, H 5.79, N 6.19; found: C78.89, H 5.72, N 5.98. (FCI/VCI, Frankfurt/Main, Germany). F.M.Y. thanks the MS [EI, m/z (%)]: 453 (40) [M]+, 452 (80) [M], 328 (30) [M − L] +, German Academic Exchange Service (DAAD, Bonn, Germany)

327 (95) [M − L], 202 (25) [diyne], 118 (100) [PhNC2H3], 77 (20) for a generous Ph.D. stipend. Infrastructure of our institute [Ph]. IR: 3051 w, 2942 w, 2909 w, 2894 w, 2821 w, 2186 w, 2186 was provided by the EU (European Regional Development w, 1946 w, 1840 w, 1582 m, 1561 m, 1502 vs, 1441 m, 1349 s, Fund, EFRE) and the Friedrich Schiller University Jena. 1295 m, 1218 s, 1094 s, 991 m, 811 s, 787 vs, 635 m, 600 s, 504 s, 472 w. 1,4-Diphenyl-1-(N-methyl-anilino)-4-(N-methyl-4-fluoroani- References lino)buta-1,3-diene (3). To a solution of N-(1,4-diphenylbut-1- en-3-yne-1yl)-N-methylaniline (1) (0.120 g, 0.38 mmol) in 15 ml 1 Recent reviews on late transition metal-catalyzed hydroami- of THF, 4-fluoro-N-methylaniline (0.048 g, 0.38 mmol) and nation: (a) L. Huang, M. Arndt, K. Goossen, H. Heydt and

5 mol% of the catalyst [K2Ca{N(H)Dipp}4] were added three L. J. Goossen, Chem. Rev., 2015, 115, 2596–2697; times every 4 days and stirred for 12 days at r.t. A standard (b) E. Bernoud, C. Lepori, M. Mellah, E. Schulz and workup procedure including hydrolysis with 20 ml of distilled J. Hannedouche, Catal. Sci. Technol., 2015, 5, 2017–2037; water, extraction with diethyl ether, drying with sodium sulfate (c) J. A. Garduno, A. Arevalo and J. J. Garcia, Dalton Trans., and recrystallization from dichloromethane/pentane at 5 °C 2015, 44, 13419–13438; (d) K. Hirano and M. Miura, Pure yields colorless crystals from a yellow solution (0.08 g, Appl. Chem., 2014, 86, 291–297; (e) K. D. Hesp, Angew. 1 0.18 mmol, 47%). M.p. 136–137 °C. H NMR (600 MHz, C6D6): Chem., Int. Ed., 2014, 53, 2034–2036; (f) J. Hannedouche

Published on 20 November 2015. Downloaded by Thueringer Universitats Landesbibliothek Jena 26/04/2016 15:01:54. δ 7.33–7.23 (m, 3H, Ar–H), 7.19–7.16 (m, 6H, Ar–H), 7.03–6.90 and E. Schulz, Chem. – Eur. J., 2013, 19, 4972–4985; (m, 8H, Ar–H), 6.82 (m, 4H, Ar–H), 6.75 (m, 1H, Ar–H), 6.65 (s, (g) N. Nishina and Y. Yamamoto, Top. Organomet. Chem., 2H, C2H, C2AH), 6.57–6.49 (m, 2H, Ar–H), 2.93 (s, 3H, C3H), 2013, 43, 115–144; (h) T. Li, S. Schulz and P. W. Roesky, 13 1 2.85 (s, 3H, C3AH). C{ H} NMR (151 MHz, C6D6) δ 156.47 (d, Chem. Soc. Rev., 2012, 41, 3759–3771; (i) K. D. Hesp and 1 4 – JC, F = 235.8 Hz, C7), 148.8, 146 (d, J = 26.7 Hz, C4), 145.2, M. Stradiotto, ChemCatChem, 2010, 2, 1192 1207; 138.6, 138.5. 129.5, 128.9, 128.9, 128.4, 127.55, 126.97, 127, ( j) A. S. K. Hashmi and C. Hubbert, Angew. Chem., Int. Ed., 120.5, 120.3, 118.2, 115.9, 115.8, 115, 114.9, 114.2, 39.3, 38.9. 2010, 49, 1010–1012. 19 δ − − F NMR (188 MHz, C6D6): 120.9 (E,Z isomer), 128 (E,E 2 General reviews: (a) J. S. Yadav, A. Antony, T. S. Rao and isomer), −129.6 (Z,E isomer). Elemental analysis (C30H27N2F, B. V. S. Reddy, J. Organomet. Chem., 2011, 696,16–36; 434.22): calc.: C 82.92, H 6.26, N 6.45, F 4.37; found: C83.25, (b) T. E. Müller, K. C. Hultzsch, M. Yus, F. Foubelo and H 5.72, N 6.40. MS [EI, m/z (%)]: 434 (100) [M], 316 (40), M. Tada, Chem. Rev., 2008, 108, 3795–3892; (c) R. Severin 309 (50) [M − L], 293 (40), 217 (75), 198 (55), 180 (40), 118 (65) and S. Doye, Chem. Soc. Rev., 2007, 36, 1407–1420;

[PhNC2H3], 77 (40) [Ph]. IR 3030 w, 2959 w, 2876 w, 2814 w, (d) F. Pohlki and S. Doye, Chem. Soc. Rev., 2003, 32, 104– 2184 m, 1582 m, 1558 m, 1490 s, 1439 m, 1333 m, 1321 m, 114. 1260 m, 1165 m, 1113 s, 1008 m, 874 m, 776 s, 758 vs, 693 vs, 3 Recent reviews on s-block metal-catalyzed hydroamination: 582 m, 516 m, 498 m, 468 s. (a) A. L. Reznichenko, A. J. Nawara-Hultzsch and K. C. Hultzsch, Top. Curr. Chem., 2014, 343, 191–260; X-Ray structure determinations (b) M. R. Crimmin and M. S. Hill, Top. Organomet. Chem., The intensity data for the compounds were collected on a 2013, 45, 191–241; (c) A. L. Reznichenko and Nonius Kappa CCD diffractometer using graphite-monochro- K. C. Hultzsch, Top. Organomet. Chem., 2013, 43,51–114;

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Calcium-Mediated Catalytic Synthesis of 1‑(Diorganylamino)-1,4- diphenyl-4-(diphenylphosphanyl)buta-1,3-dienes Fadi M. Younis, Sven Krieck, Tareq M. A. Al-Shboul,+ Helmar Görls, and Matthias Westerhausen* Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University (FSU), Humboldstraße 8, D-07743 Jena, Germany

*S Supporting Information

ABSTRACT: The hydroamination of diphenylbutadiyne with 1 equiv of the secondary amines HNRR′ (R/R′ = Ph/Ph, Ph/Me, and pTol/Me) in the presence of catalytic amounts of the tetrakis(amino)calciate K2[Ca{N(H)Dipp}4](Dipp=2,6- diisopropylphenyl) yields the corresponding 1-(diorganylami- no)-1,4-diphenylbut-1-ene-3-ynes as a mixture of E/Z isomers. These tertiary alkenylamines react with diphenylphosphane to ′ −  −  − ′ form RR N C(Ph) CH CH C(Ph) PPh2 [R/R = Ph/Ph (1), Ph/Me (2), and pTol/Me (3)] in the presence of catalytic amounts of [(THF)4Ca(PPh2)2] or of the same calciate K2[Ca{N(H)Dipp}4]. Whereas the hydroamination is regio- (amino group in 1-position) but not stereoselective (formation of E and Z isomers), this second hydrofunctionalization step is regio- (phosphanyl group in 4-position) and stereoselective (only E isomers are formed), finally leading to mixtures of (E,E)- and (Z,E)-1-(diorganylamino)-1,4-diphenyl-4-(diphenylphosphanyl)- buta-1,3-dienes.

■ INTRODUCTION tetracoordinate calcium atom fulfills these requirements and hence represents an approved catalytically active calciate Hydrofunctionalization (hydroelementation, hydropentelation) 7 resembles an atom-economic addition of H−E bonds [E being because this ether-free complex is soluble in ethereal solvents. the penteles N (hydroamination) and P (hydrophosphanyla- The reaction pathway of primary amines H2NR with tion)] to alkenes and alkynes; however, several challenges must butadiynes strongly depends on the reaction conditions and − be solved. Hydroamination and hydrophosphanylation repre- the N-bound substituent. Nevertheless, both N H bonds are sent only slightly exothermic reactions that are entropically able to add to alkyne moieties, yielding either 2,5-substituted 8 disfavored. In addition, the approach of a Lewis base (primary pyrroles at high reaction temperatures or multicyclic imines at or secondary amine and phosphane) to an electron-rich CC room temperature and prolonged reaction times.7,8 Secondary and CC multiple bond is disadvantageous and requires an amines can add only once; hence, cyclic products are effective catalyst to overcome the electrostatic repulsion. avoided.6,9 Thus, N-alkyl anilines add to one or both CC Several strategies have been developed, and recently, alkaline bonds of the butadiyne backbone, depending on the reaction earth metal-mediated hydropentelation catalysis has gained time, the stoichiometry of the substrates, and the amount of 1−3 significant interest. Calcium-based catalysts are especially calcium catalyst, yielding 1-aminobut-1-ene-3-yne or 1,4- attractive because these alkaline earth metals are globally diaminobuta-1,3-dienes, respectively. In contrast to this abundant, inexpensive, easily available, and nontoxic. observation, secondary diphenylphosphane always adds twice Intramolecular hydroamination of alkenes eliminates the to both CC bonds of the butadiyne unit in the presence of entropic disadvantage and eases the addition of H−N bonds to  catalytic amounts of [(THF)4Ca(PPh2)2] (THF = tetrahy- C C bonds. Calcium-based catalysts are able to catalyze this drofuran, Scheme 1).10 Even a large excess of butadiyne leads reaction, yielding azacycloalkanes.4 Intermolecular hydroami- to the formation of bis-phosphanylated compounds, and nation is achieved only with activated alkenes5 and is much unreacted alkyne remains in the reaction mixture. The easier with CC bonds, requiring more reactive calcium-based catalysts correlated with the risk of also promoting undesired hydrophosphanylation of substituted butadiynes with diphe- side reactions.6 The reactivity of a calcium amide can be nylphosphane yields primarily 1,4-bis(diphenylphosphanyl)- enhanced by the formation of a calciate. The catalyst should be buta-1,3-dienes; however, other regioisomers such as 1,2- coligand-free in order to avoid desolvation of the isolated bis(diphenylphosphanyl)buta-1,3-dienes have also been ob- crystalline compound due to uncontrolled loss of ligated Lewis served. Neither the hydroamination nor the hydrophosphany- bases such as ethers. This fact is important to allow an accurate ratio of catalyst to substrate. The heterobimetallic compound Received: March 8, 2016 K2[Ca{N(H)Dipp}4] (Dipp = 2,6-diisopropylphenyl) with a Published: April 15, 2016

© 2016 American Chemical Society 4676 DOI: 10.1021/acs.inorgchem.6b00586 Inorg. Chem. 2016, 55, 4676−4682 Inorganic Chemistry Article

Scheme 1. Calcium-Mediated Hydrophosphanylation of Diphenylbutadiyne with Diphenylphosphane Yielding Isomeric Mixtures of 1,4-Bis(diphenylphosphanyl)buta-1,3-dienes

lation is stereoselective, but mixtures of E and Z isomers are catalyst was destroyed with methanol. The hydropentelation formed. product 1 was recrystallized from methylene chloride/pentane, These findings suggest that the synthesis of substituted 1- giving yellow crystals of E/E-1 and Z/E-1. amino-4-phosphanylbuta-1,3-dienes requires hydroamination as In another trial, the catalytic hydrophosphanylation of 1- the initial step and hydrophosphanylation as a subsequent diphenylamino-1,4-diphenylbut-1-ene-3-yne was repeated with reaction. A further objective was the elucidation of the necessity catalytic amounts of K2[Ca{N(H)Dipp}4]. After complete to change the calcium-based catalyst from K2[Ca{N(H)Dipp}4] conversion, the solvent was removed, and the residue was for hydroamination to [(THF)4Ca(PPh2)2] for the following dissolved in methanol to inactivate the calcium catalyst. After hydrophosphanylation. On the basis of the pKa values of removal of the methanol, the residue was dissolved in arylamines (approximately 31, depending on the substitution methylene chloride and filtered to remove the calcium- pattern), N-methyl-aniline (29.5), diphenylamine (25.0), and containing compounds. Thereafter, recrystallization from 11 diphenylphosphane (22.9), the calciate K2[Ca{N(H)Dipp}4] methylene chloride/pentane again provided yellow crystals of is able to deprotonate secondary amines and diphenylphos- E/E-1 and Z/E-1 (Scheme 3). This result suggests that the two phane, which is a precondition for the suitability of this calciate as a catalyst for hydropentelation reactions. Scheme 3. Hydroamination and Hydrophosphanylation of Diphenylbutadiyne with the Same Catalyst ■ RESULTS AND DISCUSSION K2[Ca{N(H)Dipp}4] Synthesis and Catalysis. The singly hydroaminated E and Z isomers of 1-diphenylamino-1,4-diphenylbut-1-ene-3-yne9 were hydrophosphanylated with diphenylphosphane in THF in the presence of 5 mol % [(THF)4Ca(PPh2)2], quantitatively yielding 1-diphenylamino-1,4-diphenyl-4-diphenylphosphanyl- buta-1,3-diene (1)(Scheme 2). The conversion of the substrates was monitored by 31P{1H} NMR spectroscopy. The E/Z isomerism at the amino functionality was maintained, whereas only the E-isomeric hydrophosphanylation was observed. After complete reaction, the volume of the reaction mixture was reduced to half of the original volume, and the

Scheme 2. Two-Step Synthesis of 1-Diphenylamino-1,4- diphenyl-4-(diphenylphosphanyl)buta-1,3-diene (1) Using Different Calcium-Based Catalysts for the Hydropentelation Reactions different hydroelementation reactions can be performed without a change in the catalyst system and without the need to isolate the hydroamination product prior to the hydro- phosphanylation reaction. fi Because of the promising nding that K2[Ca{N(H)Dipp}4] can promote hydroamination and hydrophosphanylation of diphenylbutadiyne, the hydroamination of diphenylbutadiyne was also performed with N-methyl-aniline and N-methyl- tolylamine as previously published with the catalyst K2[Ca{N- 9 (H)Dipp}4]. Diphenylphosphane was added to this reaction mixture, yielding the appropriate hydrofunctionalization products 1-(N -methyl-anilino)-1,4-diphenyl-4- (diphenylphosphanyl)buta-1,3-diene (2)and1-(N-methyl- tolylamino)-1,4-diphenyl-4-diphenylphosphanylbuta-1,3-diene (3) according to Scheme 4. Again, the initial hydroamination reaction gave an E/Z-isomeric mixture, whereas the hydro- phosphanylation occurred regio- and stereoselectively to the E- isomeric hydrophosphanylation products.

4677 DOI: 10.1021/acs.inorgchem.6b00586 Inorg. Chem. 2016, 55, 4676−4682 Inorganic Chemistry Article

Scheme 4. Calcium-Mediated Synthesis of 1-(N- Methylanilino)-1,4-diphenyl-4-(diphenylphosphanyl)buta- a 1,3-dienes

Figure 1. Molecular structure and numbering scheme of (E,E)-1- diphenylamino-1,4-diphenyl-4-(diphenylphosphanyl)buta-1,3-diene (E,E-1). The ellipsoids represent a probability of 30%; H atoms are aAryl = phenyl (2)orp-tolyl (3). shown with arbitrary radii.

Isolation of the intermediate hydroamination product 1- amino-1,4-diphenylbut-1-ene-3-yne proved to be advantageous to prevent impurities such as bis-hydroaminated compounds. Unreacted butadiyne also had to be removed prior to the hydrophosphanylation procedures because otherwise the product would also contain bis-hydrophosphanylated deriva- tives. These side products hamper the isolation of analytically pure 1-amino-1,4-diphenyl-4-(diphenylphosphanyl)buta-1,3- diene and hence lower the yields. Therefore, the preferred method involves an initial hydroamination reaction catalyzed by fi K2[Ca{N(H)Dipp}4], followed by isolation and puri cation of 1-amino-1,4-diphenylbut-1-ene-3-yne. Thereafter, the hydro- phosphanylation of this amine can be performed using catalytic amounts of either [(THF)4Ca(PPh2)2]orK2[Ca{N(H)- Dipp}4]. In neither case were E,Z- and Z,Z-isomeric 1-amino- 1,4-diphenyl-4-(diphenylphosphanyl)buta-1,3-dienes observed. This finding is most probably the consequence of steric strain, Figure 2. Molecular structure and numbering scheme of (Z,E)-1-(N- but electronic effects may also play a minor role. methyl-anilino)-1,4-diphenyl-4-(diphenylphosphanyl)buta-1,3-diene Molecular Structures. The molecular structures of (E,E)- (Z,E-2). The ellipsoids represent a probability of 30%; H atoms are 1-diphenylamino-1,4-diphenyl-4-(diphenylphosphanyl)buta- drawn with arbitrary radii. 1,3-diene (E,E-1) and (Z,E)-1-(N-methyl-anilino)-1,4-diphen- yl-4-(diphenylphosphanyl)buta-1,3-diene (Z,E-2) are depicted in Figures 1 and 2, respectively, and the structures of Z,E-1 and and butadiene moieties in all of these compounds, representing Z,E-3 are represented in the Supporting Information. Selected a characteristic P−C single-bond value. structural parameters are compared in Table 1. Regardless of NMR Spectroscopy. Selected NMR parameters of the 1- the isomerism, the structural parameters of these compounds amino-1,4-diphenyl-4-(diphenylphosphanyl)buta-1,3-dienes are are very similar. The butadiene fragment shows no delocaliza- compared in Table 2. The E/Z isomerism of the amino group tion, and typical CCandC−C bond lengths of has a small influence on the chemical shifts of the 31P nuclei. approximately 135 and 145 pm, respectively, are observed. Thus, the 31P resonances of the E,E isomers are observed at For steric reasons, the planar amino group is twisted toward the nearly 5 ppm, whereas the Z,E isomers show chemical shifts of planar butadiene plane; therefore, the electron pair at N cannot about 2.5 ppm. The carbon atoms of the butadiene backbone interact with the π-system of the butadiene moiety. In contrast show low-field shifted signals between 135 and 156 ppm. Here, to the amino group, the phosphorus atom is in a trigonal the amino-substituted C4 atoms lie at a field lower than that of − − n pyramidal environment with C P C bond angles of about the P-bound C1 atoms. The absolute values of the JC−P 102°. Steric strain between the substituted end groups leads to coupling constants decrease with increasing n from approx- a distortion of the C−C−C bond angles of the butadiene imately 22 Hz (n = 1) over 12 Hz (n = 2) to 2 Hz (n = 3). The − − − − 3 3 fragment. The C1 C2 C3 and C2 C3 C4 bond angles of vicinal JH−H and JH−P couplings of the hydrogen atoms at C2 E,E-1 are significantly widened, whereas for all Z,E isomers, the and C3 also depend on the isomerism of the amino group with enlargement of these bond angles is smaller. This finding larger values for the E,E isomers. verifies an intramolecular steric strain of the Z,E isomers smaller In agreement with the structural data, the Z,E-isomeric forms than that of the E,E derivatives. The lack of interaction between are the major components, whereas the amount of E,E isomers the phosphanyl end groups and the butadiene units leads to is always significantly smaller. Therefore, we were able to isolate very similar P−C bonds of approximately 183 pm to the phenyl and crystallize the Z,E isomers of all reported derivatives,

4678 DOI: 10.1021/acs.inorgchem.6b00586 Inorg. Chem. 2016, 55, 4676−4682 Inorganic Chemistry Article

Table 1. Selected Structural Parameters of 1-Diphenylamino- alkenylcalcium complex A either deprotonates an amine 1,4-diphenyl-4-(diphenylphosphanyl)buta-1,3-diene (1), 1- (formation of the E-isomeric alkenylamine) or rearranges via (N-Methyl-anilino)-1,4-diphenyl-4- intermediates B and C to the finally formed Z-alkenylamine. (diphenylphosphanyl)buta-1,3-diene (2), and 1-(N-Methyl- The necessity of obtaining the monohydroaminated products D tolylamino)-1,4-diphenyl-4-(diphenylphosphanyl)buta-1,3- and E limits the substitution pattern of the secondary amine diene (3) substrates. For more reactive amines, the second calcium- mediated hydroamination of the other CC bond overlaps E,E-1 Z,E-1 Z,E-2 Z,E-3 with the first hydroamination step, yielding mixtures of starting P1−C1 182.9(2) 183.6(2) 183.5(3) 182.7(4) butadiyne and singly and doubly hydroaminated butadienes. In C1−C2 135.5(3) 134.6(2) 135.2(4) 134.0(6) our hands, the above-utilized aniline derivatives represent the C2−C3 144.6(3) 145.0(2) 144.7(4) 144.8(6) preferred substrates.9 After complete conversion and preferably C3−C4 134.9(3) 135.3(2) 135.1(4) 135.6(6) isolation of the alkenylamines, diphenylphosphane is added, N1−C4 143.3(3) 142.3(2) 142.0(4) 141.4(5) immediately yielding the catalytically active calcium phospha- P1−C5 182.0(3) 183.6(2) 183.4(3) 182.9(5) nide species (L represents Lewis bases such as anionic amides P1−C11 182.3(3) 182.9(2) 183.8(2) 182.9(4) and phosphanides or neutral amines, phosphanes, or ethers). C1−C17 148.4(3) 148.4(2) 149.3(4) 149.6(6) The addition of the newly formed Ca−P bond to the remaining C4−C23 148.7(4) 147.6(2) 148.7(4) 148.0(6) CC bond yields the intermediates F and G that immediately N1−C29 143.5(3) 141.5(2) 139.5(4) 141.2(6) deprotonate the still-present diphenylphosphane. This hydro- N1−C35 142.9(3) 142.6(2) 146.1(4) 145.0(6) phosphanylation always leads to the formation of E-isomeric − − C1 P1 C5 102.1(1) 102.10(8) 102.2(1) 103.6(2) alkenylphosphanes, as shown in Scheme 5. In contrast to the − − C1 P1 C11 102.7(1) 102.11(8) 103.8(1) 102.7(2) calcium-mediated hydroamination, the catalytic hydrophospha- − − C5 P1 C11 103.9(1) 102.44(8) 102.5(1) 103.3(2) nylation represents a very fast addition of a phosphane to an − − P1 C1 C2 122.1(2) 121.7(1) 121.8(2) 123.0(3) alkyne moiety. Under these reaction conditions, neither the − − C1 C2 C3 125.2(2) 127.7(2) 126.9(3) 126.5(4) amines nor the phosphanes react with the CC bonds. The − − C2 C3 C4 127.1(2) 122.3(2) 122.1(3) 124.8(4) sequence of the catalytic steps (first hydroamination, then − − C3 C4 N1 118.8(2) 118.8(2) 120.7(2) 120.0(4) hydrophosphanylation) must be maintained because the − − C4 N1 C29 117.3(2) 120.1(1) 120.4(2) 120.8(3) phosphanes always add quantitatively to both CC bonds, − − C4 N1 C35 117.7(2) 119.5(1) 119.5(3) 119.0(4) invariably yielding doubly hydrophosphanylated derivatives.10 C29−N1−C35 118.8(2) 120.1(1) 119.9(3) 118.8(4) ■ CONCLUSION Table 2. Selected NMR Data of the E,E and E,Z Isomers of 1-Diphenylamino-1,4-diphenyl-4- In summary, 1-amino- and 4-phosphanyl-substituted buta-1,3- (diphenylphosphanyl)buta-1,3-diene (1), 1-(N-Methyl- dienes can be prepared and isolated in moderate to good yields anilino)-1,4-diphenyl-4-(diphenylphosphanyl)buta-1,3-diene from a calcium-mediated stepwise addition of secondary amines (2), and 1-(N-Methyl-tolylamino)-1,4-diphenyl-4- and phosphanes to butadiyne. Both of these hydrofunctional- (diphenylphosphanyl)-buta-1,3-diene (3) ization reactions can be promoted with the coligand-free calciate K2[Ca{N(H)Dipp}4] that is easily accessible and stable E,E-1 Z,E-1 E,E-2 Z,E-2 E,E-3 Z,E-3 in the crystalline state as well as in ethereal solvents, allowing 1H NMR the preparation of stock solutions. After inactivation of the δ(C2-H) 6.39 6.29 6.27 6.01 6.31 6.03 catalyst with methanol, pure 1-amino-4-phosphanylbuta-1,3- δ(C3-H) 6.62 6.45 6.49 6.51 6.49 6.42 dienes are obtained by common workup procedures. Even 3J(H,H) 8.3 5.3 8.2 5.9 8.5 6.0 though the same catalyst is used for both hydroelementation 3J(H,P) 12.1 10.7 11.6 10.9 11.5 10.9 steps, the isolation of the intermediate 1-amino-1,4-diphenyl- δ (N-CH3) 3.04 2.82 2.96 2.81 but-1-ene-3-yne is recommended to ease isolation of the pure 13C{1H} NMR end products. δ(C1) 140.6 140.4 141.8 141.1 140.3 142.4 Dipotassium tetrakis(2,6-diisopropylanilino)calciate is an 1J(C,P) 23.1 23.1 19.8 22.1 22.2 22.7 easy-to-handle and effective catalyst for the hydrofunctionaliza- δ(C2) 136.4 135.0 136.2 136.2 136.1 135.5 tion of CC bonds in diphenylbutadiyne with both secondary 2J(C,P) 11.7 12.1 12.3 12.3 10.8 12.4 amines and phosphanes, allowing the synthesis of 1-amino-1,4- δ(C3) 146.7 145.7 147.5 147.5 146.6 147.0 diphenyl-4-phosphanylbuta-1,3-dienes. This calciate crystallizes 3J(C,P) 2.5 2.1 2.1 2.1 2.8 2.2 as a coordination polymer; nevertheless, it is soluble in ethereal δ(C4) 147.5 147.1 151.6 149.5 152.0 156.0 solvents, enabling the preparation of stock solutions. The δ crystalline compound and the stock solutions of this complex (N-CH3) 40.9 38.1 38 37.5 31P{1H} NMR are stable and can be stored under anaerobic conditions. Both δ(P1) 4.45 2.54 4.70 2.28 4.96 2.35 hydroelementation steps are regioselective, but only the catalytic addition of the H−P bond also stereoselectively yields the E isomer. whereas the parameters of the E,E-isomeric compounds had to be elucidated from isomeric mixtures. ■ EXPERIMENTAL SECTION Proposed Mechanism. fi On the basis of these ndings, the General Considerations. All manipulations were carried out catalytic cycle had to be formulated as a two-step reaction under nitrogen using standard Schlenk techniques. The solvents were sequence, and the proposed mechanism is presented in Scheme dried according to standard procedures prior to use. Deuterated 5. The initial catalytic cycle is depicted in the bottom part. After solvents were dried over sodium, degassed, and saturated with addition of the Ca−N bond, the intermediately formed nitrogen. The yields given are not optimized. 1H, 13C{1H}, and

4679 DOI: 10.1021/acs.inorgchem.6b00586 Inorg. Chem. 2016, 55, 4676−4682 Inorganic Chemistry Article

Scheme 5. Proposed Catalytic Cycle Shown as a Two-Step Process of Subsequent Hydroamination and Hydrophosphanylation a Reactions

aThe bottom part shows the hydroamination and offers an explanation for the Z/E isomerism. In the second hydrophosphanylation catalysis, the amido ligand is substituted by the phosphanido group. The thus-formed Ca−P bond adds to the remaining alkyne moiety, followed by a metalation reaction. L represents a Lewis base such as amido or phosphanido anions or neutral Lewis bases such as ethers, amines, and phosphanes (see text).

31P{1H} NMR spectra were recorded on Bruker Avance 200, Avance crystals was obtained and isolated. In method B, to a solution of 1- 400, and Avance 600 spectrometers. Chemical shifts are reported in diphenylamino-1,4-diphenylbut-1-ene-3-yne (0.140 g, 0.376 mmol) in parts per million. In some cases, 1H,13C{1H}-HSQC, 1H,13C{1H}- THF (18 mL) were added diphenylphosphane (0.07g, 0.376 mmol) HMBC, and H,H-COSY NMR experiments were performed for the and 5 mol % calciate K2[Ca{N(H)Dipp}4]. The reaction mixture was assignment of the resonances. For mass spectrometric investigations, stirred for 6 h at rt. Afterward, the solvent was removed in vacuo, and the spectrometers ThermoFinnigan MAT95XL and Finnigan SSQ710 10 mL of anhydrous methanol was added to inactivate the catalyst. were used. IR spectra were recorded with a Bruker ALPHA FT-IR Then, the methanol was removed, and 12 mL of dichloromethane was spectrometer. The starting amines and calcium-based catalysts added. This solution was filtered over diatomaceous earth. ff [(THF)4Ca(PPh2)2] and K2[Ca{N(H)Dipp}4] were prepared accord- Crystallization via the di usion method (dichloromethane/pentane) ing to the literature protocols. at 5 °C yielded yellow crystals suitable for X-ray diffraction studies Synthesis of 1-Diphenylamino-1,4-diphenyl-4- (0.14 g, 0.251 mmol, 67%, mixture of isomers). Mp: 138−142 °C. 1H δ (diphenylphosphanyl)buta-1,3-diene (1). In method A, 1- NMR (600 MHz, THF): 7.36 (d, JH−H = 7.2 Hz, 2H), 7.31 (JH−H = diphenylamino-1,4-diphenylbut-1-ene-3-yne (0.2 g, 0.54 mmol) was 7.7 Hz, 2H), 7.21−7.07 (m, 16H), 7.06−7.01 (m, 4H), 6.88 (m, 6H), 3 3 dissolved in 8 mL of THF. Diphenylphosphane (0.094 mL, 0.54 6.66 (d, JH−H = 7.5 Hz, 1H, E,E), 6.45 (d, JH−H = 10.7 Hz, 1H, Z,E), 3 3 mmol) and 5 mol % [(THF)4Ca(PPh2)2] were added. The reaction 6.39 (dd, JH−P = 12.1, 8.3 Hz, 1H, C2-HE,E), 6.29 (dd, JH−P = 10.7, 13 1 δ mixture turned yellow immediately. After being stirred at rt for 2 h and 5.3 Hz, 1H, C2-HZ,E). C{ H} NMR (101 MHz, CD2Cl2): 147.5 3 under reflux for an additional 6 h, the volume was reduced to half of (C4 E,E), 147.3 (C4 Z,E), 146.7 (d, JC−P = 2.5 Hz, C3 E,E), 145.9 (d, 3 the original volume. A few milliliters of methanol were added, and the JC−P = 2.4 Hz, C3 Z,E), 144 (d, JC−P = 16.5 Hz, C11,5), 143.4 (d, 2 reaction mixture was stored at −15 °C. Yellow crystals of 3 (0.11 g, 0.2 JC−P = 6.4 Hz), 140.6 (d, JC−P = 23.1 Hz, C1 E,E), 139.8 (d, JC−P = 2 2 mmol, 37%, mixture of isomers) precipitated and were collected. After 23.1 Hz, C1 Z,E), 139.5, 139 (d, JC−P = 3.5 Hz), 136.4 (d, JC−P = 2 a reduction of the volume of the mother liquor, another crop of 11.7 Hz, C2 E,E), 135 (d, JC−P = 11.6 Hz, C2 Z,E), 134.8, 134.6,

4680 DOI: 10.1021/acs.inorgchem.6b00586 Inorg. Chem. 2016, 55, 4676−4682 Inorganic Chemistry Article

2 134.18 (d, JC−P = 7.5 Hz), 133.5, 133.3, 129.8, 129.7, 129.4, 129.3, 128.2, 128.1, 127, 127.8, 126.9, 126.5, 125.8, 120, 113.7, 37.5 (C35), 3 2 13 1 129.2 (d, J = 2.8 Hz), 129.1, 128.6 (d, JC−P = 7.3 Hz), 128.4, 127.8, 19.6 (C36). C{ H} NMR (101 MHz, [D8]THF, isomeric mixture): 3 δ 3 127.7, 127.7, 127.6, 126.8, 125.5, 125.1, 122.6 (d, JC−P = 2.0 Hz), 156 (C4 Z,E), 152.8 (C4 E,E), 147.8 (d, JC−P = 2.2 Hz, C3 Z,E), 13 3 122.3, 122.2, 122.1, 122, 121.9, 121.78. C NMR (151 MHz, 146.6 (d, JC−P = 2.8 Hz, C3 E,E), 142.4 (d, JC−P = 22.7 Hz, C1 Z,E), δ 3 2 [D8]THF, Z,E isomer): 147.1 (C4), 145.7 (d, JC−P = 2.1 Hz, C3), 140.3 (d, JC−P = 22.0 Hz, C1 E,E), 139.1 (d, JC−P = 12.4 Hz, C2 Z,E), 3 2 143.9 (d, JC−P = 17.6 Hz, C11,5), 140.4 (d, JC−P = 23.1 Hz, C1), 138.5, 138.2, 136.9 (d, JC−P = 2.3 Hz), 136.1 ( JC−P = 10.8 Hz, C2 E,E), 2 2 2 135 (d, JC−P = 12.1 Hz, C2), 134.3, 134.2, 133.8 (d, JC−P = 7.9 Hz), 135.5 (d, JC−P = 12.4 Hz, C2 Z,E) 135.4, 135.2, 135.1, 134.3, 134.2, 2 2 2 129.3 (d, JC−P = 9.3 Hz), 128.8, 128.5, 128.1, 128.1, 128, 127.8, 127.1, 134.1, 133.3, 132.3, 131.9 (d, JC−P = 9.1 Hz), 131.4, 131.5 (d, JC−P = 2 31 1 3 2 127, 122 (d, JC−P = 1.7 Hz), 121.8, 121.5. P{ H} NMR (243 MHz, 5.1 Hz), 130.8 (d, JC−P = 2.7 Hz), 130.5, 130.3 (d, JC−P = 4.8 Hz), δ [D8]THF): 2.54 (s, Z,E isomer), 4.49 (s, E,E isomer). Elemental 130.1, 129.4, 129.2, 129.1, 129, 128.8, 128.5, 128.5, 128.4, 128.3, 128.2, 3 analysis (C40H32NP, 557.21): Calcd C, 86.15; H, 5.78; N, 2.51; P, 5.55. 128.1 (d, JC−P = 2.7 Hz), 128.2, 127.9, 127.8, 127.7, 127.6, 127.5, 3 Found: C, 83.79; H, 5.74; N, 2.51. MS (EI, m/z): 557 (60) [M], 389 127.4, 127.2, 127, 126.5, 125.8, 125, 120 (d, JC−P = 2.3 Hz), 119.7, − (100) [M C12H11N], 370 (10), 180 (100), 77 (25) [Ph]. IR: 3049 117.7, 117.6, 114.5, 113.6, 38 (C35 Z,E), 37.4 (C35 E,E), 19.7 (C36 31 1 δ w, 3959 w, 2920 w, 1656 m, 1630 m, 1484 s, 1432 m, 1288 m, 1258 m, Z,E), 19.6 (C36 E,E). P{ H} NMR (162 MHz, [D8]THF): 4.96 (s, 1223 s, 1174 m, 1074 s, 1024 s, 859 m, 797 s, 761 s, 740 s, 690 vs, 602 E,E isomer), 2.35 (s, PZ,E isomer). Elemental analysis (C36H32NP, m, 548 m, 496 s, 479 m. 509.60): Calcd C, 84.84; H, 6.33; N, 2.75; P, 6.08. Found: C, 84.31; H, Synthesis of 1-(N-Methyl-anilino)-1,4-diphenyl-4- 6.18; N, 2.75. MS (EI, m/z): 525 (10) [M + O], 509 (50) [M], 389 − − (diphenylphosphanyl)buta-1,3-diene (2). To a solution of 1-(N- (60) [M C8H11N], 370 (100), 322 (30) [M L], 183 (100), 118 methyl-anilino)-1,4-diphenylbut-1-ene-3-yne (0.100 g, 0.323 mmol) in (60) [PhNC2H3], 77 (25) [Ph]. IR: 3051 w, 3025 w, 2914 w, 1587 m, THF (17 mL) were added diphenylphosphane (0.06 g, 0.323 mmol) 1570 m, 1510 s, 1477 m, 1361 m, 1317 m, 1281 m, 1186 m, 1104 s, and 5 mol % calciate K2[Ca{N(H)Dipp}4]. The reaction mixture was 1027 m, 911 m, 806 s, 767 s, 742 vs, 692 vs, 596 m, 557 m, 499 s, 461 stirred for 4 h at rt. After the consumption of all starting materials, all m. volatile materials were removed in vacuo, and 10 mL of anhydrous Crystal Structure Determinations. The intensity data for the methanol was added to destroy the remaining catalyst. Afterward, the compounds were collected on a Nonius KappaCCD diffractometer methanol was removed, and 12 mL of dichloromethane was added. using graphite-monochromated Mo Kα radiation. The data were Then, the solution was filtered over diatomaceous earth. Crystal- corrected for Lorentz and polarization effects; absorption was taken − lization via the diffusion method (dichloromethane/pentane) at 5 °C into account on a semiempirical basis using multiple scans.12 14 The gave single crystals in a yellow mother liquor (0.11 g, 0.222 mmol, structures were solved by Direct Methods (SHELXS15) and refined by − ° 1 δ 2 15 69%). Mp: 146 149 C. H NMR (600 MHz, [D8]THF): 7.40 (m, full-matrix least-squares techniques against Fo (SHELXL-97). All 2H, Ar-H), 7.34 (d, J = 8.2 Hz, 1H, Ar-H), 7.31−7.13 (m, 24H, Ar-H), hydrogen atoms (with the exception of the methyl groups of C35 and 3 3 ff 6.70 (t, JH−H = 7.3 Hz, 1H, Ar-H), 6.62 (m, 2H, Ar-H), 6.51 (d, JH−H C36 of compound Z,E-3) were located by di erence Fourier synthesis 3 fi fi = 10.9 Hz, 1H,C3-H, Z,E), 6.27 (dd, JH−P = 11.6, 8.2 Hz, C2-H, E,E), and re ned isotropically. All non-hydrogen atoms were re ned − 3 15 6.05 5.97 (dd, JH−P = 10.9, 5.9 Hz, 1H, C2-H, Z,E), 3.04 (s, 1H, anisotropically. Crystallographic data as well as structure solution C35-H, Z,E), 2.82 (s, 3H, C35-H, Z,E). 13C{1H} NMR (151 MHz, and refinement details are summarized in the Supporting Information. δ 3 [D8]THF): 151.6 (C4 E,E), 149.5 (C4 Z,E), 147.5 (d, JC−P = 2.1 XP (SIEMENS Analytical X-ray Instruments, Inc.) was used for 3 1 Hz, C3 Z,E, E,E), 143.9 (d, JC−P = 7.6 Hz), 141.8 (d, JC−P = 19.8 Hz, structure representations. 1 2 C1 E,E), 141.1 (d, JC−P = 22.1 Hz, C1 Z,E), 139, 136.2 (d, JC−P = 2 12.3 Hz, C3 Z,E, E,E), 135.08 (d, JC−P = 20.6 Hz, C5,11), 134, 134.7, ■ ASSOCIATED CONTENT 2 2 134.6, 130.7, 130.3 (d, JC−P = 7.8 Hz, C17), 130.1 (d, JC−P = 8.7 Hz), *S 2 Supporting Information 129.5, 129.4, 129.2, 129.1, 129.1, 129 (d, JC−P = 4.0 Hz), 129, 128.8, 128.8, 128.7, 128.5, 128.5, 128.3, 127.9, 127.3, 127, 123.1, 122.3, 121.5, The Supporting Information is available free of charge on the 117.9, 114.2, 111.4, 40.9 (C35 E,E isomer), 38.1 (C35 Z,E isomer). ACS Publications website at DOI: 10.1021/acs.inorg- 31 1 δ chem.6b00586. Crystallographic data (excluding structure P{ H} NMR (243 MHz, [D8]THF): 4.70 (s, E,E isomer), 2.28 (s, Z,E isomer). Elemental analysis (C35H30NP, 495.57): Calcd C, 84.82; factors) have been deposited with the Cambridge Crystallo- H, 6.10; N, 2.83; P, 6.25. Found: C, 84.54; H, 6.10; N, 2.86. MS (EI, graphic Data Centre as supplementary publication CCDC- − m/z): 434 (90) [M], 389 (100) [M C7H9N], 370 (50), 309 (30) 1457771 for E,E-1, CCDC-1457772 for Z,E-1, CCDC-1457773 − [M L], 183 (90), 118 (70) [PhNC2H3], 77 (25) [Ph]. IR: 3052 w, for Z,E-2, and CCDC-1457774 for Z,E-3. 2961 w, 2815 w, 2800 w, 1950 w, 1595 m, 1541 m, 1484 s, 1432 m, 1350 m, 1321 m, 1260 m, 1199 m, 1106 s, 1009 m, 885 m, 775 s, 746 NMR spectra and details for the quantum chemical vs, 688 vs, 598 m, 505 m, 498 m, 478 s. studies (PDF) Synthesis of 1-(N-Methyl-tolylamino)-1,4-diphenyl-4- Crystallographic data of the crystal structure determi- (diphenylphosphanyl)buta-1,3-diene (3). To a solution of (N- nations (CIF) methyl)-(N-4-tolyl)-1,4-diphenylbut-1-ene-3-yne-1-ylamine (0.270 g, 0.834 mmol) in THF (17 mL) were added diphenylphosphane (0.156 ■ AUTHOR INFORMATION g, 0.834 mmol) and 5 mol % calciate catalyst K2[Ca{N(H)Dipp}4], and the reaction mixture was stirred for 8 h at rt. After the reaction Corresponding Author solvent was removed, 10 mL of dry methanol was added to deactivate *E-mail: [email protected]. the catalyst. Afterward, the methanol was removed; 12 mL of Present Address dichloromethane was added, and the solution was filtered over Celite. + ff T.M.A.A.: Department of Chemistry and Chemical Technol- Recrystallization via the di usion method (dichloromethane/pentane) fi at 5 °C yielded crystals in a yellow solution (0.3 g, 0.588 mmol, 71%). ogy, Faculty of Science, Ta la Technical University (TTU), − ° 1 δ − P.O. Box 179, Tafila 66110, Jordan. Mp: 147 152 C. H NMR (400 MHz, [D8]THF): 7.43 7.34 (m, − − 2H), 7.30 7.10 (m, 18H), 6.99 (d, JH−H = 8.2 Hz, 2H), 6.60 6.50 (m, Notes 3 3 2H), 6.49 (d, JH‑H = 7.6 Hz, 1H, C3-HE,E), 6.42 (d, JH‑H = 10.9 Hz, The authors declare no competing financial interest. 3 1H, C3-H Z,E), 6.31 (dd, JH−P = 11.5, 8.5 Hz, 1H, C2-HE,E), 6.03 3 (dd, JH−P = 10.9, 6.0 Hz, 1H, C2-HZ,E), 2.96 (s, 3H, C35-H E,E), ■ ACKNOWLEDGMENTS 2.81 (s, 3H, C35-H Z,E), 2.27 (s, 3H, C36-H E,E), 2.25 (s, 3H, C36-H 13 1 δ fi Z,E). C{ H} NMR (101 MHz, [D8]THF, Z,E isomer): 156.2 (C4), We appreciate the nancial support of the Fonds der 3 147 (d, JC−P = 2.2 Hz, C3), 142.4 (d, JC−P = 22.3 Hz, C1), 138.4, Chemischen Industrie im Verband der Chemischen Industrie 2 135.5 (d, JC−P = 12.4 Hz, C2), 134.5, 134, 129.3, 129.2, 128.5, 128.3, e.V. (FCI/VCI, Frankfurt/Main, Germany). F.M.Y. thanks the

4681 DOI: 10.1021/acs.inorgchem.6b00586 Inorg. Chem. 2016, 55, 4676−4682 Inorganic Chemistry Article

German Academic Exchange Service (DAAD, Bonn, Germany) for a generous Ph.D. stipend. The infrastructure of our institute was partially provided by the EU (European Regional Development Fund, EFRE). ■ REFERENCES (1) Harder, S. Chem. Rev. 2010, 110, 3852−3876. (2) (a) Hill, M. S.; Liptrot, D. J.; Weetman, C. Chem. Soc. Rev. 2016, 45, 972−988. (b) Crimmin, M. R.; Hill, M. S. Top. Organomet. Chem. 2013, 45, 191−242. (c) Barrett, A. G. M.; Crimmin, M. R.; Hill, M. S.; Procopiou, P. A. Proc. R. Soc. London, Ser. A 2010, 466, 927−963. (3) (a) Arrowsmith, M. In The Lightest Metals: Science and Technology from Lithium to Calcium; Hanusa, T. P., Ed.; Wiley: Chichester, U.K., 2015; pp 255−280. (b) Reznichenko, A. L.; Hultzsch, K. C. Top. Organomet. Chem. 2011, 43,51−114. (c) Müller, T. E.; Hultzsch, K. C.; Yus, M.; Foubelo, F.; Tada, M. Chem. Rev. 2008, 108, 3795−3892. (4) (a) Romero, N.; Rosca,̧ S.-C.; Sarazin, Y.; Carpentier, J.-F.; Vendier, L.; Mallet-Ladeira, S.; Dinoi, C.; Etienne, M. Chem. - Eur. J. 2015, 21, 4115−4125. (b) Liu, B.; Roisnel, T.; Carpentier, J. F.; Sarazin, Y. Chem. - Eur. J. 2013, 19, 2784−2802. (c) Wixey, J. S.; Ward, B. D. Chem. Commun. 2011, 47, 5449−5451. (d) Wixey, J. S.; Ward, B. D. Dalton Trans. 2011, 40, 7693−7696. (e) Mukherjee, A.; Nembenna, S.; Sen, T. K.; Sarish, S. P.; Ghorai, P. K.; Ott, H.; Stalke, D.; Mandal, S. K.; Roesky, H. W. Angew. Chem., Int. Ed. 2011, 50, 3968−3972. (f) Arrowsmith, M.; Crimmin, M. R.; Barrett, A. G. M.; Hill, M. S.; Kociok-Köhn, G.; Procopiou, P. A. Organometallics 2011, 30, 1493− 1506. (g) Neal, S. R.; Ellern, A.; Sadow, A. D. J. Organomet. Chem. 2011, 696, 228−234. (h) Crimmin, M. R.; Arrowsmith, M.; Barrett, A. G. M.; Casely, I. J.; Hill, M. S.; Procopiou, P. A. J. Am. Chem. Soc. 2009, 131, 9670−9685. (i) Barrett, A. G. M.; Crimmin, M. R.; Hill, M. S.; Hitchcock, P. B.; Kociok-Köhn, G.; Procopiou, P. A. Inorg. Chem. 2008, 47, 7366−7376. (j) Panda, T. K.; Hrib, C. G.; Jones, P. G.; Jenter, J.; Roesky, P. W.; Tamm, M. Eur. J. Inorg. Chem. 2008, 2008, 4270−4279. (k) Crimmin, M. R.; Casely, I. J.; Hill, M. S. J. Am. Chem. Soc. 2005, 127, 2042−2043. (5) (a) Brinkmann, C.; Barrett, A. G. M.; Hill, M. S.; Procopiou, P. A. J. Am. Chem. Soc. 2012, 134, 2193−2207. (b) Liu, B.; Roisnel, T.; Carpentier, J.-F.; Sarazin, Y. Angew. Chem., Int. Ed. 2012, 51, 4943− 4946. (6) Glock, C.; Görls, H.; Westerhausen, M. Chem. Commun. 2012, 48, 7094−7096. (7) Glock, C.; Younis, F. M.; Ziemann, S.; Görls, H.; Imhof, W.; Krieck, S.; Westerhausen, M. Organometallics 2013, 32, 2649−2660. (8) Younis, F. M.; Krieck, S.; Görls, H.; Westerhausen, M. Organometallics 2015, 34, 3577−3585. (9) Younis, F. M.; Krieck, S.; Görls, H.; Westerhausen, M. Dalton Trans. 2016, 45, 6241−6250. (10) (a) Al-Shboul, T. M. A.; Palfi,́ V. K.; Yu, L.; Kretschmer, R.; Wimmer, K.; Fischer, R.; Görls, H.; Reiher, M.; Westerhausen, M. J. Organomet. Chem. 2011, 696, 216−227. (b) Al-Shboul, T. M. A.; Görls, H.; Westerhausen, M. Inorg. Chem. Commun. 2008, 11, 1419− 1421. (11) Li, J.-N.; Liu, L.; Fu, Y.; Guo, Q.-X. Tetrahedron 2006, 62, 4453−4462. (12) COLLECT, Data Collection Software; Nonius B.V.: Delft, The Netherlands, 1998. (13) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data Collected in Oscillation Mode. In Methods in Enzymology; Carter, C. W., Sweet, R. M., Eds.; Macromolecular Crystallography, Part A; Academic Press: San Diego, CA, 1997; Vol. 276, pp 307−326. (14) SADABS, version 2.10; Bruker-AXS Inc.: Madison, WI, 2002. (15) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122.

4682 DOI: 10.1021/acs.inorgchem.6b00586 Inorg. Chem. 2016, 55, 4676−4682 Curriculum Vitae| 163

9 Curriculum Vitae

Personal data Name: Fadi Younis Date of birth: 24.05.1988 Place of birth: Damascus Nationality: Syrian Marital status: Single Father: Mouafak Younis, born at 10.01.1957 in Damascus, Syria Mother: Fatima Almawardy, born at 25.06.1962 in Damascus, Syria E-Mail: [email protected] [email protected] Address: Moritz-Seebeck Str. 15 07745 Jena, Germany

Educational history

x January/2012 Friedrich-Schiller-Universität Jena, Germany Ph.D., student, chemistry with Prof. Dr. M. Westerhausen

x September/2007-2011 Tishreen University, Syria Post graduated, Applied Chemistry, and Rating: (good) Date of graduation: September 2011

x July 2007 Alsaadeh Secondary School, General Secondary Education Certificate, Syria, percentage average 80%

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Practical experience

x Properties of (d) elements and their compounds and complexes 2008. x Automatic analysis, part (1, 2) at Tishreen University, Syria 2009. x Three months research with laboratory techniques in Friedrich-Schiller- University, Jena, Germany, summer 2010, organized by IAESTE. x Employee at the scientific office in Sultan Company for Hygiene & Disinfection, Translating scientific articles about various disinfectants from English into Arabic. Doing scientific studies on sterilizing substances, like comparing the effectiveness and characteristics of wounds sterilizing materials, supervising the application of sterilizing materials in many hospitals in Damascus 2011. x Course about laboratory management (October, 2011) at Damascus university. x Since 2012 supervising master and bachelor students in different topics such as (organometallic catalytic synthesis as well as organic and inorganic compounds) at Friedrich-Schiller-University, Jena, Germany. x 2015 two months short term research in Universidade Federal De Viçosa, Brazil.

Awards x Excellence graduated (certified as Academic excellence). 2009 x Scholarship for exchange students (DAAD), I.A.E.S.T.E. -Germany, July/2010. x DAAD grant for Ph.D. research April/2013 x I.A.E.S.T.E. Germany certificate as member 2014/2015/2016 x Short-term scholarship (DAAD), I.A.E.S.T.E. -Brazil, October/2015.

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Languages Arabic: native language.

Other languages

Language Understand Speaking writing ing English Very good Very good Very good German Very good Very good Very good Portuguese Basic Basic Basic

Research interests Metal-organic chemistry, metal-mediated catalysis.

References x Prof. Dr. Matthias Westerhausen, Prof. Friedrich-Schiller-Universität Jena E-Mail: [email protected] Tel.: +49 3641 948110 x Prof. Dr. Rainer Beckert, Prof. Friedrich-Schiller-Universität Jena E-Mail: [email protected] Tel.: +49 3641 9 48 230 x Prof. Dr. Jose Roberto Maia, Prof. Universidade Federal De Viçosa, Brazil E-Mail: [email protected] Tel.: +55 (31) 3899 3059

x Prof. Mohammad Y. El-Khateeb, Prof. Jordan University of Science & Technology, Jordan E-mail: [email protected] Tel.: (+962)2-7201000- (Ext: 23644) x Prof. Dr. Khalid Shawakfah, Prof. Jordan University of Science & Technology, Jordan E-mail: [email protected] Tel.: +962-27201000 - (Ext. 23646) x Dr. Moeen Noman, Associate Prof. Tishreen University, Syria E-mail: [email protected] Tel.: +963-947 781757

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Publications

1. Jens Langer, Tareq M. A. Al-Shboul, Fadi M. Younis, Helmar Görls, Matthias Westerhausen, Coordination Behavior and Coligand-Dependent cis/trans Isomerism of Calcium Bis(diphenylphosphanides). Eur. J. Inorg. Chem. (2011), 3002-3007. 2. Fadi M. Younis, Helmar Görls, Sven Krieck, Matthias Westerhausen. Synthesis and structural characterization of bis(tetrahydropyran)calciumbis[ bis(tri-methylsilyl)amide]. Z. Anorg. Allg. Chem. 2013, 19-21 3. Carsten Glock§, Fadi M. Younis§, Steffen Ziemann, Helmar Görls, Wolfgang Imhof, Sven Krieck, Matthias Westerhausen. 2,6- Diisopropylphenylamides of Potassium and Calcium A Primary Amido Ligand in s-Block Metal Chemistry with an Astonishing Reactivity. Organometallics 2013, 32, 2649-2660 4. Fadi. M. Younis, S. Krieck, H. Görls, M. Westerhausen. S-Block-Metal- Mediated Hydroamination of Diphenylbutadiyne with Primary Arylamines Using a Dipotassium Tetrakis(amino)calciate Precatalyst. Organometallics 2015, 34, 3577-3585. 5. Fadi. M. Younis, S. Krieck, H. Görls, M. Westerhausen. Hydroamination of diphenylbutadiyne with secondary N-methyl-anilines using the dipotassium tetrakis(2,6-diisopropylanilino)calciate precatalyst. Dalton Trans., 2016, 45, 6241-6250. 6. Fadi. M. Younis, S. Krieck, T.M. A. Al-shboul, H. Görls, M. Westerhausen. Calcium-Mediated Catalytic Synthesis of 1-(Diorganylamino)-1,4-diphenyl- 4-(diphenylphosphanyl)buta-1,3-dienes. Inorg. Chem. 2016, 55, 4676-4682.

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Conferences

x Congress: The Sixth Jordanian International Conference of Chemistry. Date: 19-22 April 2011. Place: Irbid, Jordan. x Congress: M.A.N.S-10 (Mitteldeutsches Anorganisches Nachwuchs Symposium) Date: 20 September 2012. Place: Jena, Germany. x Congress: M.A.N.S-11 (Mitteldeutsches Anorganisches Nachwuchs Symposium) Date: 19 September 2013 (Lecturer). Place: Dresden, Germany. x I.A.E.S.T.E. national conference 2012, 2013, 2014, 2015, Bonn, Germany. x I.A.E.S.T.E. local committees meeting 2012, 2013, 2014, 2016 (Cologne, Hamburg, Chemnitz, Freiberg), Germany. x Congress: M.A.N.S-13 (Mitteldeutsches Anorganisches Nachwuchs Symposium) Date: September 2015. Place: Chemnitz, Germany.

Personal Merits

Self-motivated, Positive attitude, Willingness to Learn, Open Minded, Social, work under pressure, patient, Responsible and committed to excellence and success, Multicultural awareness and ambitious. Habits

Reading, cycling, hiking, swimming, traveling, learning about cultures and languages.

Selbstständigkeitserklärung| 168

10 Selbstständigkeitserklärung

Ich erkläre, dass ich die vorliegende Arbeit selbständig und unter Verwendung der angegebenen Hilfsmittel, persönlichen Mitteilungen und Quellen angefertigt habe.

Jena, den «««««««««« Fadi Younis